[v6,04/51] drm/bridge: Add connector-related bridge operations and data
diff mbox series

Message ID 20200216210308.17312-5-laurent.pinchart@ideasonboard.com
State New
Headers show
Series
  • drm/omap: Replace custom display drivers with drm_bridge and drm_panel
Related show

Commit Message

Laurent Pinchart Feb. 16, 2020, 9:02 p.m. UTC
To support implementation of DRM connectors on top of DRM bridges
instead of by bridges, the drm_bridge needs to expose new operations and
data:

- Output detection, hot-plug notification, mode retrieval and EDID
  retrieval operations
- Bitmask of supported operations
- Bridge output type
- I2C adapter for DDC access

Add and document these.

Three new bridge helper functions are also added to handle hot plug
notification in a way that is as transparent as possible for the
bridges.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
---
Changes since v3:

- Fix typos

Changes since v2:

- Add wrappers around the .detect(), .get_modes() and .get_edid()
  operations
- Warn bridge drivers about valid usage of the connector argument to
  .get_modes() and .get_edid()

Changes since v1:

- Make .hpd_enable() and .hpd_disable() optional
- Rename .lost_hotplug() to .hpd_notify()
- Add ddc field to drm_bridge
---
 drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++
 include/drm/drm_bridge.h     | 192 ++++++++++++++++++++++++++++++++++-
 2 files changed, 353 insertions(+), 1 deletion(-)

Comments

Daniel Vetter Feb. 17, 2020, 9:53 a.m. UTC | #1
On Sun, Feb 16, 2020 at 11:02:21PM +0200, Laurent Pinchart wrote:
> To support implementation of DRM connectors on top of DRM bridges
> instead of by bridges, the drm_bridge needs to expose new operations and
> data:
> 
> - Output detection, hot-plug notification, mode retrieval and EDID
>   retrieval operations
> - Bitmask of supported operations
> - Bridge output type
> - I2C adapter for DDC access
> 
> Add and document these.
> 
> Three new bridge helper functions are also added to handle hot plug
> notification in a way that is as transparent as possible for the
> bridges.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
> ---
> Changes since v3:
> 
> - Fix typos
> 
> Changes since v2:
> 
> - Add wrappers around the .detect(), .get_modes() and .get_edid()
>   operations
> - Warn bridge drivers about valid usage of the connector argument to
>   .get_modes() and .get_edid()
> 
> Changes since v1:
> 
> - Make .hpd_enable() and .hpd_disable() optional
> - Rename .lost_hotplug() to .hpd_notify()
> - Add ddc field to drm_bridge
> ---
>  drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++
>  include/drm/drm_bridge.h     | 192 ++++++++++++++++++++++++++++++++++-
>  2 files changed, 353 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 68ab933ee430..78d26a9a3ee6 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -71,6 +71,8 @@ static LIST_HEAD(bridge_list);
>   */
>  void drm_bridge_add(struct drm_bridge *bridge)
>  {
> +	mutex_init(&bridge->hpd_mutex);
> +
>  	mutex_lock(&bridge_lock);
>  	list_add_tail(&bridge->list, &bridge_list);
>  	mutex_unlock(&bridge_lock);
> @@ -87,6 +89,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
>  	mutex_lock(&bridge_lock);
>  	list_del_init(&bridge->list);
>  	mutex_unlock(&bridge_lock);
> +
> +	mutex_destroy(&bridge->hpd_mutex);
>  }
>  EXPORT_SYMBOL(drm_bridge_remove);
>  
> @@ -919,6 +923,164 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
>  }
>  EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
>  
> +/**
> + * drm_bridge_detect - check if anything is attached to the bridge output
> + * @bridge: bridge control structure
> + *
> + * If the bridge supports output detection, as reported by the
> + * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
> + * bridge and return the connection status. Otherwise return
> + * connector_status_unknown.
> + *
> + * RETURNS:
> + * The detection status on success, or connector_status_unknown if the bridge
> + * doesn't support output detection.
> + */
> +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge)
> +{
> +	if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
> +		return connector_status_unknown;
> +
> +	return bridge->funcs->detect(bridge);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_detect);
> +
> +/**
> + * drm_bridge_get_modes - fill all modes currently valid for the sink into the
> + * @connector
> + * @bridge: bridge control structure
> + * @connector: the connector to fill with modes
> + *
> + * If the bridge supports output modes retrieval, as reported by the
> + * DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
> + * fill the connector with all valid modes and return the number of modes
> + * added. Otherwise return 0.
> + *
> + * RETURNS:
> + * The number of modes added to the connector.
> + */
> +int drm_bridge_get_modes(struct drm_bridge *bridge,
> +			 struct drm_connector *connector)
> +{
> +	if (!(bridge->ops & DRM_BRIDGE_OP_MODES))
> +		return 0;
> +
> +	return bridge->funcs->get_modes(bridge, connector);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_get_modes);
> +
> +/**
> + * drm_bridge_get_edid - get the EDID data of the connected display
> + * @bridge: bridge control structure
> + * @connector: the connector to read EDID for
> + *
> + * If the bridge supports output EDID retrieval, as reported by the
> + * DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
> + * get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
> + *
> + * RETURNS:
> + * The retrieved EDID on success, or an error pointer otherwise.
> + */
> +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> +				 struct drm_connector *connector)
> +{
> +	if (!(bridge->ops & DRM_BRIDGE_OP_EDID))
> +		return ERR_PTR(-ENOTSUPP);
> +
> +	return bridge->funcs->get_edid(bridge, connector);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_get_edid);
> +
> +/**
> + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
> + * @bridge: bridge control structure
> + * @cb: hot-plug detection callback
> + * @data: data to be passed to the hot-plug detection callback
> + *
> + * Call &drm_bridge_funcs.hpd_enable if implemented and register the given @cb
> + * and @data as hot plug notification callback. From now on the @cb will be
> + * called with @data when an output status change is detected by the bridge,
> + * until hot plug notification gets disabled with drm_bridge_hpd_disable().
> + *
> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> + * bridge->ops. This function shall not be called when the flag is not set.
> + *
> + * Only one hot plug detection callback can be registered at a time, it is an
> + * error to call this function when hot plug detection is already enabled for
> + * the bridge.
> + */
> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> +			   void (*cb)(void *data,
> +				      enum drm_connector_status status),
> +			   void *data)
> +{
> +	if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))

Supplying a NULL bridge is a caller bug imo, and you're inconsistent in
handling this. Imo just drop.

> +		return;
> +
> +	mutex_lock(&bridge->hpd_mutex);
> +
> +	if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
> +		goto unlock;
> +
> +	bridge->hpd_cb = cb;
> +	bridge->hpd_data = data;
> +
> +	if (bridge->funcs->hpd_enable)
> +		bridge->funcs->hpd_enable(bridge);
> +
> +unlock:
> +	mutex_unlock(&bridge->hpd_mutex);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
> +
> +/**
> + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
> + * @bridge: bridge control structure
> + *
> + * Call &drm_bridge_funcs.hpd_disable if implemented and unregister the hot
> + * plug detection callback previously registered with drm_bridge_hpd_enable().
> + * Once this function returns the callback will not be called by the bridge
> + * when an output status change occurs.
> + *
> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> + * bridge->ops. This function shall not be called when the flag is not set.
> + */
> +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
> +{
> +	if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> +		return;
> +
> +	mutex_lock(&bridge->hpd_mutex);
> +	if (bridge->funcs->hpd_disable)
> +		bridge->funcs->hpd_disable(bridge);
> +
> +	bridge->hpd_cb = NULL;
> +	bridge->hpd_data = NULL;
> +	mutex_unlock(&bridge->hpd_mutex);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
> +
> +/**
> + * drm_bridge_hpd_notify - notify hot plug detection events
> + * @bridge: bridge control structure
> + * @status: output connection status
> + *
> + * Bridge drivers shall call this function to report hot plug events when they
> + * detect a change in the output status, when hot plug detection has been
> + * enabled by drm_bridge_hpd_enable().
> + *
> + * This function shall be called in a context that can sleep.
> + */
> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> +			   enum drm_connector_status status)
> +{
> +	mutex_lock(&bridge->hpd_mutex);
> +	if (bridge->hpd_cb)
> +		bridge->hpd_cb(bridge->hpd_data, status);
> +	mutex_unlock(&bridge->hpd_mutex);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
> +
>  #ifdef CONFIG_OF
>  /**
>   * of_drm_find_bridge - find the bridge corresponding to the device node in
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 45626ecf20f8..ba9b7c84f11e 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -23,8 +23,9 @@
>  #ifndef __DRM_BRIDGE_H__
>  #define __DRM_BRIDGE_H__
>  
> -#include <linux/list.h>
>  #include <linux/ctype.h>
> +#include <linux/list.h>
> +#include <linux/mutex.h>
>  
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_encoder.h>
> @@ -33,7 +34,10 @@
>  
>  struct drm_bridge;
>  struct drm_bridge_timings;
> +struct drm_connector;
>  struct drm_panel;
> +struct edid;
> +struct i2c_adapter;
>  
>  /**
>   * struct drm_bridge_funcs - drm_bridge control functions
> @@ -488,6 +492,119 @@ struct drm_bridge_funcs {
>  	 * giving the reason of the failure otherwise.
>  	 */
>  	struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
> +
> +	/**
> +	 * @detect:
> +	 *
> +	 * Check if anything is attached to the bridge output.
> +	 *
> +	 * This callback is optional, if not implemented the bridge will be
> +	 * considered as always having a component attached to its output.
> +	 * Bridges that implement this callback shall set the
> +	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * drm_connector_status indicating the bridge output status.
> +	 */
> +	enum drm_connector_status (*detect)(struct drm_bridge *bridge);
> +
> +	/**
> +	 * @get_modes:
> +	 *
> +	 * Fill all modes currently valid for the sink into the &drm_connector
> +	 * with drm_mode_probed_add().
> +	 *
> +	 * The @get_modes callback is mostly intended to support non-probeable
> +	 * displays such as many fixed panels. Bridges that support reading
> +	 * EDID shall leave @get_modes unimplemented and implement the
> +	 * &drm_bridge_funcs->get_edid callback instead.
> +	 *
> +	 * This callback is optional. Bridges that implement it shall set the
> +	 * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
> +	 *
> +	 * The connector parameter shall be used for the sole purpose of
> +	 * filling modes, and shall not be stored internally by bridge drivers
> +	 * for future usage.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * The number of modes added by calling drm_mode_probed_add().
> +	 */
> +	int (*get_modes)(struct drm_bridge *bridge,
> +			 struct drm_connector *connector);
> +
> +	/**
> +	 * @get_edid:
> +	 *
> +	 * Read and parse the EDID data of the connected display.
> +	 *
> +	 * The @get_edid callback is the preferred way of reporting mode
> +	 * information for a display connected to the bridge output. Bridges
> +	 * that support reading EDID shall implement this callback and leave
> +	 * the @get_modes callback unimplemented.
> +	 *
> +	 * The caller of this operation shall first verify the output
> +	 * connection status and refrain from reading EDID from a disconnected
> +	 * output.
> +	 *
> +	 * This callback is optional. Bridges that implement it shall set the
> +	 * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
> +	 *
> +	 * The connector parameter shall be used for the sole purpose of EDID
> +	 * retrieval and parsing, and shall not be stored internally by bridge
> +	 * drivers for future usage.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * An edid structure newly allocated with kmalloc() (or similar) on
> +	 * success, or NULL otherwise. The caller is responsible for freeing
> +	 * the returned edid structure with kfree().
> +	 */
> +	struct edid *(*get_edid)(struct drm_bridge *bridge,
> +				 struct drm_connector *connector);
> +
> +	/**
> +	 * @hpd_notify:
> +	 *
> +	 * Notify the bridge of hot plug detection.
> +	 *
> +	 * This callback is optional, it may be implemented by bridges that
> +	 * need to be notified of display connection or disconnection for
> +	 * internal reasons. One use case is to reset the internal state of CEC
> +	 * controllers for HDMI bridges.
> +	 */
> +	void (*hpd_notify)(struct drm_bridge *bridge,
> +			   enum drm_connector_status status);
> +
> +	/**
> +	 * @hpd_enable:
> +	 *
> +	 * Enable hot plug detection. From now on the bridge shall call
> +	 * drm_bridge_hpd_notify() each time a change is detected in the output
> +	 * connection status, until hot plug detection gets disabled with
> +	 * @hpd_disable.
> +	 *
> +	 * This callback is optional and shall only be implemented by bridges
> +	 * that support hot-plug notification without polling. Bridges that
> +	 * implement it shall also implement the @hpd_disable callback and set
> +	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> +	 */
> +	void (*hpd_enable)(struct drm_bridge *bridge);
> +
> +	/**
> +	 * @hpd_disable:
> +	 *
> +	 * Disable hot plug detection. Once this function returns the bridge
> +	 * shall not call drm_bridge_hpd_notify() when a change in the output
> +	 * connection status occurs.
> +	 *
> +	 * This callback is optional and shall only be implemented by bridges
> +	 * that support hot-plug notification without polling. Bridges that
> +	 * implement it shall also implement the @hpd_enable callback and set
> +	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> +	 */
> +	void (*hpd_disable)(struct drm_bridge *bridge);
>  };
>  
>  /**
> @@ -526,6 +643,39 @@ struct drm_bridge_timings {
>  	bool dual_link;
>  };
>  
> +/**
> + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
> + */
> +enum drm_bridge_ops {
> +	/**
> +	 * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
> +	 * its output. Bridges that set this flag shall implement the
> +	 * &drm_bridge_funcs->detect callback.
> +	 */
> +	DRM_BRIDGE_OP_DETECT = BIT(0),
> +	/**
> +	 * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
> +	 * connected to its output. Bridges that set this flag shall implement
> +	 * the &drm_bridge_funcs->get_edid callback.
> +	 */
> +	DRM_BRIDGE_OP_EDID = BIT(1),
> +	/**
> +	 * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
> +	 * without requiring polling. Bridges that set this flag shall
> +	 * implement the &drm_bridge_funcs->hpd_enable and
> +	 * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
> +	 * and disabling hot-plug detection dynamically.
> +	 */
> +	DRM_BRIDGE_OP_HPD = BIT(2),
> +	/**
> +	 * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
> +	 * by the display at its output. This does not include reading EDID
> +	 * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
> +	 * this flag shall implement the &drm_bridge_funcs->get_modes callback.
> +	 */
> +	DRM_BRIDGE_OP_MODES = BIT(3),
> +};

I still don't like this one here, since most of them are tracking
redundant information. If you don't like just checking for the hook
directly wrap it in a helper, e.g.

bool drm_bridge_supports_detect(bridge)
{
	return bridge->ops->detect;
}

hpd seems to be special, since a bridge can support hotplug but not have
the enable_hpd/disable_hpd hooks. Which smells somewhat fishy, since if
you have multiple bridges with hpd, how do you make sure you get hpd
events only from the right one?

Aside from that just having a

	bool supports_hpd;

seems a lot simpler.

Yes I know that the drm DRIVER_FOO flags don't work like that, and I'm
kinda unhappy about them since forever. Managed to delete most of them
even :-)

Cheers, Daniel

> +
>  /**
>   * struct drm_bridge - central DRM bridge control structure
>   */
> @@ -554,6 +704,33 @@ struct drm_bridge {
>  	const struct drm_bridge_funcs *funcs;
>  	/** @driver_private: pointer to the bridge driver's internal context */
>  	void *driver_private;
> +	/** @ops: bitmask of operations supported by the bridge */
> +	enum drm_bridge_ops ops;
> +	/**
> +	 * @type: Type of the connection at the bridge output
> +	 * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
> +	 * identifies the type of connected display.
> +	 */
> +	int type;
> +	/**
> +	 * @ddc: Associated I2C adapter for DDC access, if any.
> +	 */
> +	struct i2c_adapter *ddc;
> +	/** private: */
> +	/**
> +	 * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
> +	 */
> +	struct mutex hpd_mutex;
> +	/**
> +	 * @hpd_cb: Hot plug detection callback, registered with
> +	 * drm_bridge_hpd_enable().
> +	 */
> +	void (*hpd_cb)(void *data, enum drm_connector_status status);
> +	/**
> +	 * @hpd_data: Private data passed to the Hot plug detection callback
> +	 * @hpd_cb.
> +	 */
> +	void *hpd_data;
>  };
>  
>  static inline struct drm_bridge *
> @@ -660,6 +837,19 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
>  					u32 output_fmt,
>  					unsigned int *num_input_fmts);
>  
> +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
> +int drm_bridge_get_modes(struct drm_bridge *bridge,
> +			 struct drm_connector *connector);
> +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> +				 struct drm_connector *connector);
> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> +			   void (*cb)(void *data,
> +				      enum drm_connector_status status),
> +			   void *data);
> +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> +			   enum drm_connector_status status);
> +
>  #ifdef CONFIG_DRM_PANEL_BRIDGE
>  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
>  struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,
> -- 
> Regards,
> 
> Laurent Pinchart
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
Laurent Pinchart Feb. 18, 2020, 1:21 a.m. UTC | #2
Hi Daniel,

On Mon, Feb 17, 2020 at 10:53:08AM +0100, Daniel Vetter wrote:
> On Sun, Feb 16, 2020 at 11:02:21PM +0200, Laurent Pinchart wrote:
> > To support implementation of DRM connectors on top of DRM bridges
> > instead of by bridges, the drm_bridge needs to expose new operations and
> > data:
> > 
> > - Output detection, hot-plug notification, mode retrieval and EDID
> >   retrieval operations
> > - Bitmask of supported operations
> > - Bridge output type
> > - I2C adapter for DDC access
> > 
> > Add and document these.
> > 
> > Three new bridge helper functions are also added to handle hot plug
> > notification in a way that is as transparent as possible for the
> > bridges.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
> > ---
> > Changes since v3:
> > 
> > - Fix typos
> > 
> > Changes since v2:
> > 
> > - Add wrappers around the .detect(), .get_modes() and .get_edid()
> >   operations
> > - Warn bridge drivers about valid usage of the connector argument to
> >   .get_modes() and .get_edid()
> > 
> > Changes since v1:
> > 
> > - Make .hpd_enable() and .hpd_disable() optional
> > - Rename .lost_hotplug() to .hpd_notify()
> > - Add ddc field to drm_bridge
> > ---
> >  drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++
> >  include/drm/drm_bridge.h     | 192 ++++++++++++++++++++++++++++++++++-
> >  2 files changed, 353 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > index 68ab933ee430..78d26a9a3ee6 100644
> > --- a/drivers/gpu/drm/drm_bridge.c
> > +++ b/drivers/gpu/drm/drm_bridge.c
> > @@ -71,6 +71,8 @@ static LIST_HEAD(bridge_list);
> >   */
> >  void drm_bridge_add(struct drm_bridge *bridge)
> >  {
> > +	mutex_init(&bridge->hpd_mutex);
> > +
> >  	mutex_lock(&bridge_lock);
> >  	list_add_tail(&bridge->list, &bridge_list);
> >  	mutex_unlock(&bridge_lock);
> > @@ -87,6 +89,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
> >  	mutex_lock(&bridge_lock);
> >  	list_del_init(&bridge->list);
> >  	mutex_unlock(&bridge_lock);
> > +
> > +	mutex_destroy(&bridge->hpd_mutex);
> >  }
> >  EXPORT_SYMBOL(drm_bridge_remove);
> >  
> > @@ -919,6 +923,164 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
> >  }
> >  EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
> >  
> > +/**
> > + * drm_bridge_detect - check if anything is attached to the bridge output
> > + * @bridge: bridge control structure
> > + *
> > + * If the bridge supports output detection, as reported by the
> > + * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
> > + * bridge and return the connection status. Otherwise return
> > + * connector_status_unknown.
> > + *
> > + * RETURNS:
> > + * The detection status on success, or connector_status_unknown if the bridge
> > + * doesn't support output detection.
> > + */
> > +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge)
> > +{
> > +	if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
> > +		return connector_status_unknown;
> > +
> > +	return bridge->funcs->detect(bridge);
> > +}
> > +EXPORT_SYMBOL_GPL(drm_bridge_detect);
> > +
> > +/**
> > + * drm_bridge_get_modes - fill all modes currently valid for the sink into the
> > + * @connector
> > + * @bridge: bridge control structure
> > + * @connector: the connector to fill with modes
> > + *
> > + * If the bridge supports output modes retrieval, as reported by the
> > + * DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
> > + * fill the connector with all valid modes and return the number of modes
> > + * added. Otherwise return 0.
> > + *
> > + * RETURNS:
> > + * The number of modes added to the connector.
> > + */
> > +int drm_bridge_get_modes(struct drm_bridge *bridge,
> > +			 struct drm_connector *connector)
> > +{
> > +	if (!(bridge->ops & DRM_BRIDGE_OP_MODES))
> > +		return 0;
> > +
> > +	return bridge->funcs->get_modes(bridge, connector);
> > +}
> > +EXPORT_SYMBOL_GPL(drm_bridge_get_modes);
> > +
> > +/**
> > + * drm_bridge_get_edid - get the EDID data of the connected display
> > + * @bridge: bridge control structure
> > + * @connector: the connector to read EDID for
> > + *
> > + * If the bridge supports output EDID retrieval, as reported by the
> > + * DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
> > + * get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
> > + *
> > + * RETURNS:
> > + * The retrieved EDID on success, or an error pointer otherwise.
> > + */
> > +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> > +				 struct drm_connector *connector)
> > +{
> > +	if (!(bridge->ops & DRM_BRIDGE_OP_EDID))
> > +		return ERR_PTR(-ENOTSUPP);
> > +
> > +	return bridge->funcs->get_edid(bridge, connector);
> > +}
> > +EXPORT_SYMBOL_GPL(drm_bridge_get_edid);
> > +
> > +/**
> > + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
> > + * @bridge: bridge control structure
> > + * @cb: hot-plug detection callback
> > + * @data: data to be passed to the hot-plug detection callback
> > + *
> > + * Call &drm_bridge_funcs.hpd_enable if implemented and register the given @cb
> > + * and @data as hot plug notification callback. From now on the @cb will be
> > + * called with @data when an output status change is detected by the bridge,
> > + * until hot plug notification gets disabled with drm_bridge_hpd_disable().
> > + *
> > + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> > + * bridge->ops. This function shall not be called when the flag is not set.
> > + *
> > + * Only one hot plug detection callback can be registered at a time, it is an
> > + * error to call this function when hot plug detection is already enabled for
> > + * the bridge.
> > + */
> > +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > +			   void (*cb)(void *data,
> > +				      enum drm_connector_status status),
> > +			   void *data)
> > +{
> > +	if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> 
> Supplying a NULL bridge is a caller bug imo, and you're inconsistent in
> handling this. Imo just drop.

Sounds good to me, I'll drop it.

> > +		return;
> > +
> > +	mutex_lock(&bridge->hpd_mutex);
> > +
> > +	if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
> > +		goto unlock;
> > +
> > +	bridge->hpd_cb = cb;
> > +	bridge->hpd_data = data;
> > +
> > +	if (bridge->funcs->hpd_enable)
> > +		bridge->funcs->hpd_enable(bridge);
> > +
> > +unlock:
> > +	mutex_unlock(&bridge->hpd_mutex);
> > +}
> > +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
> > +
> > +/**
> > + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
> > + * @bridge: bridge control structure
> > + *
> > + * Call &drm_bridge_funcs.hpd_disable if implemented and unregister the hot
> > + * plug detection callback previously registered with drm_bridge_hpd_enable().
> > + * Once this function returns the callback will not be called by the bridge
> > + * when an output status change occurs.
> > + *
> > + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> > + * bridge->ops. This function shall not be called when the flag is not set.
> > + */
> > +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
> > +{
> > +	if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> > +		return;
> > +
> > +	mutex_lock(&bridge->hpd_mutex);
> > +	if (bridge->funcs->hpd_disable)
> > +		bridge->funcs->hpd_disable(bridge);
> > +
> > +	bridge->hpd_cb = NULL;
> > +	bridge->hpd_data = NULL;
> > +	mutex_unlock(&bridge->hpd_mutex);
> > +}
> > +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
> > +
> > +/**
> > + * drm_bridge_hpd_notify - notify hot plug detection events
> > + * @bridge: bridge control structure
> > + * @status: output connection status
> > + *
> > + * Bridge drivers shall call this function to report hot plug events when they
> > + * detect a change in the output status, when hot plug detection has been
> > + * enabled by drm_bridge_hpd_enable().
> > + *
> > + * This function shall be called in a context that can sleep.
> > + */
> > +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > +			   enum drm_connector_status status)
> > +{
> > +	mutex_lock(&bridge->hpd_mutex);
> > +	if (bridge->hpd_cb)
> > +		bridge->hpd_cb(bridge->hpd_data, status);
> > +	mutex_unlock(&bridge->hpd_mutex);
> > +}
> > +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
> > +
> >  #ifdef CONFIG_OF
> >  /**
> >   * of_drm_find_bridge - find the bridge corresponding to the device node in
> > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > index 45626ecf20f8..ba9b7c84f11e 100644
> > --- a/include/drm/drm_bridge.h
> > +++ b/include/drm/drm_bridge.h
> > @@ -23,8 +23,9 @@
> >  #ifndef __DRM_BRIDGE_H__
> >  #define __DRM_BRIDGE_H__
> >  
> > -#include <linux/list.h>
> >  #include <linux/ctype.h>
> > +#include <linux/list.h>
> > +#include <linux/mutex.h>
> >  
> >  #include <drm/drm_atomic.h>
> >  #include <drm/drm_encoder.h>
> > @@ -33,7 +34,10 @@
> >  
> >  struct drm_bridge;
> >  struct drm_bridge_timings;
> > +struct drm_connector;
> >  struct drm_panel;
> > +struct edid;
> > +struct i2c_adapter;
> >  
> >  /**
> >   * struct drm_bridge_funcs - drm_bridge control functions
> > @@ -488,6 +492,119 @@ struct drm_bridge_funcs {
> >  	 * giving the reason of the failure otherwise.
> >  	 */
> >  	struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
> > +
> > +	/**
> > +	 * @detect:
> > +	 *
> > +	 * Check if anything is attached to the bridge output.
> > +	 *
> > +	 * This callback is optional, if not implemented the bridge will be
> > +	 * considered as always having a component attached to its output.
> > +	 * Bridges that implement this callback shall set the
> > +	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * drm_connector_status indicating the bridge output status.
> > +	 */
> > +	enum drm_connector_status (*detect)(struct drm_bridge *bridge);
> > +
> > +	/**
> > +	 * @get_modes:
> > +	 *
> > +	 * Fill all modes currently valid for the sink into the &drm_connector
> > +	 * with drm_mode_probed_add().
> > +	 *
> > +	 * The @get_modes callback is mostly intended to support non-probeable
> > +	 * displays such as many fixed panels. Bridges that support reading
> > +	 * EDID shall leave @get_modes unimplemented and implement the
> > +	 * &drm_bridge_funcs->get_edid callback instead.
> > +	 *
> > +	 * This callback is optional. Bridges that implement it shall set the
> > +	 * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
> > +	 *
> > +	 * The connector parameter shall be used for the sole purpose of
> > +	 * filling modes, and shall not be stored internally by bridge drivers
> > +	 * for future usage.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * The number of modes added by calling drm_mode_probed_add().
> > +	 */
> > +	int (*get_modes)(struct drm_bridge *bridge,
> > +			 struct drm_connector *connector);
> > +
> > +	/**
> > +	 * @get_edid:
> > +	 *
> > +	 * Read and parse the EDID data of the connected display.
> > +	 *
> > +	 * The @get_edid callback is the preferred way of reporting mode
> > +	 * information for a display connected to the bridge output. Bridges
> > +	 * that support reading EDID shall implement this callback and leave
> > +	 * the @get_modes callback unimplemented.
> > +	 *
> > +	 * The caller of this operation shall first verify the output
> > +	 * connection status and refrain from reading EDID from a disconnected
> > +	 * output.
> > +	 *
> > +	 * This callback is optional. Bridges that implement it shall set the
> > +	 * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
> > +	 *
> > +	 * The connector parameter shall be used for the sole purpose of EDID
> > +	 * retrieval and parsing, and shall not be stored internally by bridge
> > +	 * drivers for future usage.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * An edid structure newly allocated with kmalloc() (or similar) on
> > +	 * success, or NULL otherwise. The caller is responsible for freeing
> > +	 * the returned edid structure with kfree().
> > +	 */
> > +	struct edid *(*get_edid)(struct drm_bridge *bridge,
> > +				 struct drm_connector *connector);
> > +
> > +	/**
> > +	 * @hpd_notify:
> > +	 *
> > +	 * Notify the bridge of hot plug detection.
> > +	 *
> > +	 * This callback is optional, it may be implemented by bridges that
> > +	 * need to be notified of display connection or disconnection for
> > +	 * internal reasons. One use case is to reset the internal state of CEC
> > +	 * controllers for HDMI bridges.
> > +	 */
> > +	void (*hpd_notify)(struct drm_bridge *bridge,
> > +			   enum drm_connector_status status);
> > +
> > +	/**
> > +	 * @hpd_enable:
> > +	 *
> > +	 * Enable hot plug detection. From now on the bridge shall call
> > +	 * drm_bridge_hpd_notify() each time a change is detected in the output
> > +	 * connection status, until hot plug detection gets disabled with
> > +	 * @hpd_disable.
> > +	 *
> > +	 * This callback is optional and shall only be implemented by bridges
> > +	 * that support hot-plug notification without polling. Bridges that
> > +	 * implement it shall also implement the @hpd_disable callback and set
> > +	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> > +	 */
> > +	void (*hpd_enable)(struct drm_bridge *bridge);
> > +
> > +	/**
> > +	 * @hpd_disable:
> > +	 *
> > +	 * Disable hot plug detection. Once this function returns the bridge
> > +	 * shall not call drm_bridge_hpd_notify() when a change in the output
> > +	 * connection status occurs.
> > +	 *
> > +	 * This callback is optional and shall only be implemented by bridges
> > +	 * that support hot-plug notification without polling. Bridges that
> > +	 * implement it shall also implement the @hpd_enable callback and set
> > +	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> > +	 */
> > +	void (*hpd_disable)(struct drm_bridge *bridge);
> >  };
> >  
> >  /**
> > @@ -526,6 +643,39 @@ struct drm_bridge_timings {
> >  	bool dual_link;
> >  };
> >  
> > +/**
> > + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
> > + */
> > +enum drm_bridge_ops {
> > +	/**
> > +	 * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
> > +	 * its output. Bridges that set this flag shall implement the
> > +	 * &drm_bridge_funcs->detect callback.
> > +	 */
> > +	DRM_BRIDGE_OP_DETECT = BIT(0),
> > +	/**
> > +	 * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
> > +	 * connected to its output. Bridges that set this flag shall implement
> > +	 * the &drm_bridge_funcs->get_edid callback.
> > +	 */
> > +	DRM_BRIDGE_OP_EDID = BIT(1),
> > +	/**
> > +	 * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
> > +	 * without requiring polling. Bridges that set this flag shall
> > +	 * implement the &drm_bridge_funcs->hpd_enable and
> > +	 * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
> > +	 * and disabling hot-plug detection dynamically.
> > +	 */
> > +	DRM_BRIDGE_OP_HPD = BIT(2),
> > +	/**
> > +	 * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
> > +	 * by the display at its output. This does not include reading EDID
> > +	 * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
> > +	 * this flag shall implement the &drm_bridge_funcs->get_modes callback.
> > +	 */
> > +	DRM_BRIDGE_OP_MODES = BIT(3),
> > +};
> 
> I still don't like this one here, since most of them are tracking
> redundant information. If you don't like just checking for the hook
> directly wrap it in a helper, e.g.
> 
> bool drm_bridge_supports_detect(bridge)
> {
> 	return bridge->ops->detect;
> }

It seems I've done a really bad job explaining why the flags are
required, so let me try again :-)

There's a difference between supporting an operation in a driver, and
supporting it in a given system. When a bridge hardware supports reading
EDID, or detecting hotplug, the driver will implement this and expose
the corresponding operation in drm_bridge_funcs by setting the function
pointers appropriately.

However, this doesn't mean that the DDC lines are wired to the bridge on
a particular board, they could be connected to an I2C controller of the
SoC. Same for the HPD line, it could be connected to a GPIO instead of a
dedicated pin of the bridge. This board-specific information is reported
by the firmware (ACPI or DT), parsed by the bridge driver, and reflected
in the drm_bridge_ops flags.

drm_bridge_funcs and drm_bridge_ops are thus different, the latter
supplements the former. We could merge the two by setting the
corresponding function pointer in drm_bridge_funcs to NULL when the
drm_bridge_ops flag isn't set. This would however require allocating
drm_bridge_funcs dynamically (either by embedding it into a
driver-specific structure, or allocating it dynamically directly)
instead of using a global static const struct, and this is considered to
be a security issue as it allows a potential attacker to overwrite
function pointers (there have been quite a lot of security patches
merged that move function pointers to .rodata or otherwise const
memory).

> hpd seems to be special, since a bridge can support hotplug but not have
> the enable_hpd/disable_hpd hooks. Which smells somewhat fishy, since if
> you have multiple bridges with hpd, how do you make sure you get hpd
> events only from the right one?

On a given board HPD should only be generated by one bridge in practice.
If we ever encounter systems where multiple bridges can generate HPD for
the same external HPD event, I think we can deal with them at that time.

> Aside from that just having a
> 
> 	bool supports_hpd;
> 
> seems a lot simpler.

If we only needed DRM_BRIDGE_OP_HPD, I agree that a bool would be
simpler, but as explained above we need the other ones too :-)

> Yes I know that the drm DRIVER_FOO flags don't work like that, and I'm
> kinda unhappy about them since forever. Managed to delete most of them
> even :-)
> 
> > +
> >  /**
> >   * struct drm_bridge - central DRM bridge control structure
> >   */
> > @@ -554,6 +704,33 @@ struct drm_bridge {
> >  	const struct drm_bridge_funcs *funcs;
> >  	/** @driver_private: pointer to the bridge driver's internal context */
> >  	void *driver_private;
> > +	/** @ops: bitmask of operations supported by the bridge */
> > +	enum drm_bridge_ops ops;
> > +	/**
> > +	 * @type: Type of the connection at the bridge output
> > +	 * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
> > +	 * identifies the type of connected display.
> > +	 */
> > +	int type;
> > +	/**
> > +	 * @ddc: Associated I2C adapter for DDC access, if any.
> > +	 */
> > +	struct i2c_adapter *ddc;
> > +	/** private: */
> > +	/**
> > +	 * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
> > +	 */
> > +	struct mutex hpd_mutex;
> > +	/**
> > +	 * @hpd_cb: Hot plug detection callback, registered with
> > +	 * drm_bridge_hpd_enable().
> > +	 */
> > +	void (*hpd_cb)(void *data, enum drm_connector_status status);
> > +	/**
> > +	 * @hpd_data: Private data passed to the Hot plug detection callback
> > +	 * @hpd_cb.
> > +	 */
> > +	void *hpd_data;
> >  };
> >  
> >  static inline struct drm_bridge *
> > @@ -660,6 +837,19 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
> >  					u32 output_fmt,
> >  					unsigned int *num_input_fmts);
> >  
> > +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
> > +int drm_bridge_get_modes(struct drm_bridge *bridge,
> > +			 struct drm_connector *connector);
> > +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> > +				 struct drm_connector *connector);
> > +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > +			   void (*cb)(void *data,
> > +				      enum drm_connector_status status),
> > +			   void *data);
> > +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
> > +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > +			   enum drm_connector_status status);
> > +
> >  #ifdef CONFIG_DRM_PANEL_BRIDGE
> >  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
> >  struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,
Daniel Vetter Feb. 18, 2020, 6:44 a.m. UTC | #3
On Tue, Feb 18, 2020 at 2:21 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Daniel,
>
> On Mon, Feb 17, 2020 at 10:53:08AM +0100, Daniel Vetter wrote:
> > On Sun, Feb 16, 2020 at 11:02:21PM +0200, Laurent Pinchart wrote:
> > > To support implementation of DRM connectors on top of DRM bridges
> > > instead of by bridges, the drm_bridge needs to expose new operations and
> > > data:
> > >
> > > - Output detection, hot-plug notification, mode retrieval and EDID
> > >   retrieval operations
> > > - Bitmask of supported operations
> > > - Bridge output type
> > > - I2C adapter for DDC access
> > >
> > > Add and document these.
> > >
> > > Three new bridge helper functions are also added to handle hot plug
> > > notification in a way that is as transparent as possible for the
> > > bridges.
> > >
> > > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > > Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
> > > ---
> > > Changes since v3:
> > >
> > > - Fix typos
> > >
> > > Changes since v2:
> > >
> > > - Add wrappers around the .detect(), .get_modes() and .get_edid()
> > >   operations
> > > - Warn bridge drivers about valid usage of the connector argument to
> > >   .get_modes() and .get_edid()
> > >
> > > Changes since v1:
> > >
> > > - Make .hpd_enable() and .hpd_disable() optional
> > > - Rename .lost_hotplug() to .hpd_notify()
> > > - Add ddc field to drm_bridge
> > > ---
> > >  drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++
> > >  include/drm/drm_bridge.h     | 192 ++++++++++++++++++++++++++++++++++-
> > >  2 files changed, 353 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > > index 68ab933ee430..78d26a9a3ee6 100644
> > > --- a/drivers/gpu/drm/drm_bridge.c
> > > +++ b/drivers/gpu/drm/drm_bridge.c
> > > @@ -71,6 +71,8 @@ static LIST_HEAD(bridge_list);
> > >   */
> > >  void drm_bridge_add(struct drm_bridge *bridge)
> > >  {
> > > +   mutex_init(&bridge->hpd_mutex);
> > > +
> > >     mutex_lock(&bridge_lock);
> > >     list_add_tail(&bridge->list, &bridge_list);
> > >     mutex_unlock(&bridge_lock);
> > > @@ -87,6 +89,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
> > >     mutex_lock(&bridge_lock);
> > >     list_del_init(&bridge->list);
> > >     mutex_unlock(&bridge_lock);
> > > +
> > > +   mutex_destroy(&bridge->hpd_mutex);
> > >  }
> > >  EXPORT_SYMBOL(drm_bridge_remove);
> > >
> > > @@ -919,6 +923,164 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
> > >  }
> > >  EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
> > >
> > > +/**
> > > + * drm_bridge_detect - check if anything is attached to the bridge output
> > > + * @bridge: bridge control structure
> > > + *
> > > + * If the bridge supports output detection, as reported by the
> > > + * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
> > > + * bridge and return the connection status. Otherwise return
> > > + * connector_status_unknown.
> > > + *
> > > + * RETURNS:
> > > + * The detection status on success, or connector_status_unknown if the bridge
> > > + * doesn't support output detection.
> > > + */
> > > +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge)
> > > +{
> > > +   if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
> > > +           return connector_status_unknown;
> > > +
> > > +   return bridge->funcs->detect(bridge);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_detect);
> > > +
> > > +/**
> > > + * drm_bridge_get_modes - fill all modes currently valid for the sink into the
> > > + * @connector
> > > + * @bridge: bridge control structure
> > > + * @connector: the connector to fill with modes
> > > + *
> > > + * If the bridge supports output modes retrieval, as reported by the
> > > + * DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
> > > + * fill the connector with all valid modes and return the number of modes
> > > + * added. Otherwise return 0.
> > > + *
> > > + * RETURNS:
> > > + * The number of modes added to the connector.
> > > + */
> > > +int drm_bridge_get_modes(struct drm_bridge *bridge,
> > > +                    struct drm_connector *connector)
> > > +{
> > > +   if (!(bridge->ops & DRM_BRIDGE_OP_MODES))
> > > +           return 0;
> > > +
> > > +   return bridge->funcs->get_modes(bridge, connector);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_get_modes);
> > > +
> > > +/**
> > > + * drm_bridge_get_edid - get the EDID data of the connected display
> > > + * @bridge: bridge control structure
> > > + * @connector: the connector to read EDID for
> > > + *
> > > + * If the bridge supports output EDID retrieval, as reported by the
> > > + * DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
> > > + * get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
> > > + *
> > > + * RETURNS:
> > > + * The retrieved EDID on success, or an error pointer otherwise.
> > > + */
> > > +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> > > +                            struct drm_connector *connector)
> > > +{
> > > +   if (!(bridge->ops & DRM_BRIDGE_OP_EDID))
> > > +           return ERR_PTR(-ENOTSUPP);
> > > +
> > > +   return bridge->funcs->get_edid(bridge, connector);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_get_edid);
> > > +
> > > +/**
> > > + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
> > > + * @bridge: bridge control structure
> > > + * @cb: hot-plug detection callback
> > > + * @data: data to be passed to the hot-plug detection callback
> > > + *
> > > + * Call &drm_bridge_funcs.hpd_enable if implemented and register the given @cb
> > > + * and @data as hot plug notification callback. From now on the @cb will be
> > > + * called with @data when an output status change is detected by the bridge,
> > > + * until hot plug notification gets disabled with drm_bridge_hpd_disable().
> > > + *
> > > + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> > > + * bridge->ops. This function shall not be called when the flag is not set.
> > > + *
> > > + * Only one hot plug detection callback can be registered at a time, it is an
> > > + * error to call this function when hot plug detection is already enabled for
> > > + * the bridge.
> > > + */
> > > +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > > +                      void (*cb)(void *data,
> > > +                                 enum drm_connector_status status),
> > > +                      void *data)
> > > +{
> > > +   if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> >
> > Supplying a NULL bridge is a caller bug imo, and you're inconsistent in
> > handling this. Imo just drop.
>
> Sounds good to me, I'll drop it.
>
> > > +           return;
> > > +
> > > +   mutex_lock(&bridge->hpd_mutex);
> > > +
> > > +   if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
> > > +           goto unlock;
> > > +
> > > +   bridge->hpd_cb = cb;
> > > +   bridge->hpd_data = data;
> > > +
> > > +   if (bridge->funcs->hpd_enable)
> > > +           bridge->funcs->hpd_enable(bridge);
> > > +
> > > +unlock:
> > > +   mutex_unlock(&bridge->hpd_mutex);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
> > > +
> > > +/**
> > > + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
> > > + * @bridge: bridge control structure
> > > + *
> > > + * Call &drm_bridge_funcs.hpd_disable if implemented and unregister the hot
> > > + * plug detection callback previously registered with drm_bridge_hpd_enable().
> > > + * Once this function returns the callback will not be called by the bridge
> > > + * when an output status change occurs.
> > > + *
> > > + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> > > + * bridge->ops. This function shall not be called when the flag is not set.
> > > + */
> > > +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
> > > +{
> > > +   if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> > > +           return;
> > > +
> > > +   mutex_lock(&bridge->hpd_mutex);
> > > +   if (bridge->funcs->hpd_disable)
> > > +           bridge->funcs->hpd_disable(bridge);
> > > +
> > > +   bridge->hpd_cb = NULL;
> > > +   bridge->hpd_data = NULL;
> > > +   mutex_unlock(&bridge->hpd_mutex);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
> > > +
> > > +/**
> > > + * drm_bridge_hpd_notify - notify hot plug detection events
> > > + * @bridge: bridge control structure
> > > + * @status: output connection status
> > > + *
> > > + * Bridge drivers shall call this function to report hot plug events when they
> > > + * detect a change in the output status, when hot plug detection has been
> > > + * enabled by drm_bridge_hpd_enable().
> > > + *
> > > + * This function shall be called in a context that can sleep.
> > > + */
> > > +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > > +                      enum drm_connector_status status)
> > > +{
> > > +   mutex_lock(&bridge->hpd_mutex);
> > > +   if (bridge->hpd_cb)
> > > +           bridge->hpd_cb(bridge->hpd_data, status);
> > > +   mutex_unlock(&bridge->hpd_mutex);
> > > +}
> > > +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
> > > +
> > >  #ifdef CONFIG_OF
> > >  /**
> > >   * of_drm_find_bridge - find the bridge corresponding to the device node in
> > > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > > index 45626ecf20f8..ba9b7c84f11e 100644
> > > --- a/include/drm/drm_bridge.h
> > > +++ b/include/drm/drm_bridge.h
> > > @@ -23,8 +23,9 @@
> > >  #ifndef __DRM_BRIDGE_H__
> > >  #define __DRM_BRIDGE_H__
> > >
> > > -#include <linux/list.h>
> > >  #include <linux/ctype.h>
> > > +#include <linux/list.h>
> > > +#include <linux/mutex.h>
> > >
> > >  #include <drm/drm_atomic.h>
> > >  #include <drm/drm_encoder.h>
> > > @@ -33,7 +34,10 @@
> > >
> > >  struct drm_bridge;
> > >  struct drm_bridge_timings;
> > > +struct drm_connector;
> > >  struct drm_panel;
> > > +struct edid;
> > > +struct i2c_adapter;
> > >
> > >  /**
> > >   * struct drm_bridge_funcs - drm_bridge control functions
> > > @@ -488,6 +492,119 @@ struct drm_bridge_funcs {
> > >      * giving the reason of the failure otherwise.
> > >      */
> > >     struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
> > > +
> > > +   /**
> > > +    * @detect:
> > > +    *
> > > +    * Check if anything is attached to the bridge output.
> > > +    *
> > > +    * This callback is optional, if not implemented the bridge will be
> > > +    * considered as always having a component attached to its output.
> > > +    * Bridges that implement this callback shall set the
> > > +    * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
> > > +    *
> > > +    * RETURNS:
> > > +    *
> > > +    * drm_connector_status indicating the bridge output status.
> > > +    */
> > > +   enum drm_connector_status (*detect)(struct drm_bridge *bridge);
> > > +
> > > +   /**
> > > +    * @get_modes:
> > > +    *
> > > +    * Fill all modes currently valid for the sink into the &drm_connector
> > > +    * with drm_mode_probed_add().
> > > +    *
> > > +    * The @get_modes callback is mostly intended to support non-probeable
> > > +    * displays such as many fixed panels. Bridges that support reading
> > > +    * EDID shall leave @get_modes unimplemented and implement the
> > > +    * &drm_bridge_funcs->get_edid callback instead.
> > > +    *
> > > +    * This callback is optional. Bridges that implement it shall set the
> > > +    * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
> > > +    *
> > > +    * The connector parameter shall be used for the sole purpose of
> > > +    * filling modes, and shall not be stored internally by bridge drivers
> > > +    * for future usage.
> > > +    *
> > > +    * RETURNS:
> > > +    *
> > > +    * The number of modes added by calling drm_mode_probed_add().
> > > +    */
> > > +   int (*get_modes)(struct drm_bridge *bridge,
> > > +                    struct drm_connector *connector);
> > > +
> > > +   /**
> > > +    * @get_edid:
> > > +    *
> > > +    * Read and parse the EDID data of the connected display.
> > > +    *
> > > +    * The @get_edid callback is the preferred way of reporting mode
> > > +    * information for a display connected to the bridge output. Bridges
> > > +    * that support reading EDID shall implement this callback and leave
> > > +    * the @get_modes callback unimplemented.
> > > +    *
> > > +    * The caller of this operation shall first verify the output
> > > +    * connection status and refrain from reading EDID from a disconnected
> > > +    * output.
> > > +    *
> > > +    * This callback is optional. Bridges that implement it shall set the
> > > +    * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
> > > +    *
> > > +    * The connector parameter shall be used for the sole purpose of EDID
> > > +    * retrieval and parsing, and shall not be stored internally by bridge
> > > +    * drivers for future usage.
> > > +    *
> > > +    * RETURNS:
> > > +    *
> > > +    * An edid structure newly allocated with kmalloc() (or similar) on
> > > +    * success, or NULL otherwise. The caller is responsible for freeing
> > > +    * the returned edid structure with kfree().
> > > +    */
> > > +   struct edid *(*get_edid)(struct drm_bridge *bridge,
> > > +                            struct drm_connector *connector);
> > > +
> > > +   /**
> > > +    * @hpd_notify:
> > > +    *
> > > +    * Notify the bridge of hot plug detection.
> > > +    *
> > > +    * This callback is optional, it may be implemented by bridges that
> > > +    * need to be notified of display connection or disconnection for
> > > +    * internal reasons. One use case is to reset the internal state of CEC
> > > +    * controllers for HDMI bridges.
> > > +    */
> > > +   void (*hpd_notify)(struct drm_bridge *bridge,
> > > +                      enum drm_connector_status status);
> > > +
> > > +   /**
> > > +    * @hpd_enable:
> > > +    *
> > > +    * Enable hot plug detection. From now on the bridge shall call
> > > +    * drm_bridge_hpd_notify() each time a change is detected in the output
> > > +    * connection status, until hot plug detection gets disabled with
> > > +    * @hpd_disable.
> > > +    *
> > > +    * This callback is optional and shall only be implemented by bridges
> > > +    * that support hot-plug notification without polling. Bridges that
> > > +    * implement it shall also implement the @hpd_disable callback and set
> > > +    * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> > > +    */
> > > +   void (*hpd_enable)(struct drm_bridge *bridge);
> > > +
> > > +   /**
> > > +    * @hpd_disable:
> > > +    *
> > > +    * Disable hot plug detection. Once this function returns the bridge
> > > +    * shall not call drm_bridge_hpd_notify() when a change in the output
> > > +    * connection status occurs.
> > > +    *
> > > +    * This callback is optional and shall only be implemented by bridges
> > > +    * that support hot-plug notification without polling. Bridges that
> > > +    * implement it shall also implement the @hpd_enable callback and set
> > > +    * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> > > +    */
> > > +   void (*hpd_disable)(struct drm_bridge *bridge);
> > >  };
> > >
> > >  /**
> > > @@ -526,6 +643,39 @@ struct drm_bridge_timings {
> > >     bool dual_link;
> > >  };
> > >
> > > +/**
> > > + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
> > > + */
> > > +enum drm_bridge_ops {
> > > +   /**
> > > +    * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
> > > +    * its output. Bridges that set this flag shall implement the
> > > +    * &drm_bridge_funcs->detect callback.
> > > +    */
> > > +   DRM_BRIDGE_OP_DETECT = BIT(0),
> > > +   /**
> > > +    * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
> > > +    * connected to its output. Bridges that set this flag shall implement
> > > +    * the &drm_bridge_funcs->get_edid callback.
> > > +    */
> > > +   DRM_BRIDGE_OP_EDID = BIT(1),
> > > +   /**
> > > +    * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
> > > +    * without requiring polling. Bridges that set this flag shall
> > > +    * implement the &drm_bridge_funcs->hpd_enable and
> > > +    * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
> > > +    * and disabling hot-plug detection dynamically.
> > > +    */
> > > +   DRM_BRIDGE_OP_HPD = BIT(2),
> > > +   /**
> > > +    * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
> > > +    * by the display at its output. This does not include reading EDID
> > > +    * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
> > > +    * this flag shall implement the &drm_bridge_funcs->get_modes callback.
> > > +    */
> > > +   DRM_BRIDGE_OP_MODES = BIT(3),
> > > +};
> >
> > I still don't like this one here, since most of them are tracking
> > redundant information. If you don't like just checking for the hook
> > directly wrap it in a helper, e.g.
> >
> > bool drm_bridge_supports_detect(bridge)
> > {
> >       return bridge->ops->detect;
> > }
>
> It seems I've done a really bad job explaining why the flags are
> required, so let me try again :-)
>
> There's a difference between supporting an operation in a driver, and
> supporting it in a given system. When a bridge hardware supports reading
> EDID, or detecting hotplug, the driver will implement this and expose
> the corresponding operation in drm_bridge_funcs by setting the function
> pointers appropriately.
>
> However, this doesn't mean that the DDC lines are wired to the bridge on
> a particular board, they could be connected to an I2C controller of the
> SoC. Same for the HPD line, it could be connected to a GPIO instead of a
> dedicated pin of the bridge. This board-specific information is reported
> by the firmware (ACPI or DT), parsed by the bridge driver, and reflected
> in the drm_bridge_ops flags.
>
> drm_bridge_funcs and drm_bridge_ops are thus different, the latter
> supplements the former. We could merge the two by setting the
> corresponding function pointer in drm_bridge_funcs to NULL when the
> drm_bridge_ops flag isn't set. This would however require allocating
> drm_bridge_funcs dynamically (either by embedding it into a
> driver-specific structure, or allocating it dynamically directly)
> instead of using a global static const struct, and this is considered to
> be a security issue as it allows a potential attacker to overwrite
> function pointers (there have been quite a lot of security patches
> merged that move function pointers to .rodata or otherwise const
> memory).

Hm so I'm pretty sure you've explained this to me already (at least!)
once in the past, and your favorite context-free & stateless reviewer
didn't bother to remember :-)

I think it's time to improve the intro DOC: section with a few special
notes on chaining bridges. That didn't happen ever since the original
bridge stuff landed, and that non-working idea from years ago evolved
a lot with all this work now. I think adding an entire sub-section or
separate DOC comment for this, which maybe also links to the
connector-bridge helper and kinda ties the entire story you guys
developed together would be really good. Otherwise I'm pretty sure
this is not going to be the last time you have to explain this to
someone ...

Cheers, Daniel

> > hpd seems to be special, since a bridge can support hotplug but not have
> > the enable_hpd/disable_hpd hooks. Which smells somewhat fishy, since if
> > you have multiple bridges with hpd, how do you make sure you get hpd
> > events only from the right one?
>
> On a given board HPD should only be generated by one bridge in practice.
> If we ever encounter systems where multiple bridges can generate HPD for
> the same external HPD event, I think we can deal with them at that time.
>
> > Aside from that just having a
> >
> >       bool supports_hpd;
> >
> > seems a lot simpler.
>
> If we only needed DRM_BRIDGE_OP_HPD, I agree that a bool would be
> simpler, but as explained above we need the other ones too :-)
>
> > Yes I know that the drm DRIVER_FOO flags don't work like that, and I'm
> > kinda unhappy about them since forever. Managed to delete most of them
> > even :-)
> >
> > > +
> > >  /**
> > >   * struct drm_bridge - central DRM bridge control structure
> > >   */
> > > @@ -554,6 +704,33 @@ struct drm_bridge {
> > >     const struct drm_bridge_funcs *funcs;
> > >     /** @driver_private: pointer to the bridge driver's internal context */
> > >     void *driver_private;
> > > +   /** @ops: bitmask of operations supported by the bridge */
> > > +   enum drm_bridge_ops ops;
> > > +   /**
> > > +    * @type: Type of the connection at the bridge output
> > > +    * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
> > > +    * identifies the type of connected display.
> > > +    */
> > > +   int type;
> > > +   /**
> > > +    * @ddc: Associated I2C adapter for DDC access, if any.
> > > +    */
> > > +   struct i2c_adapter *ddc;
> > > +   /** private: */
> > > +   /**
> > > +    * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
> > > +    */
> > > +   struct mutex hpd_mutex;
> > > +   /**
> > > +    * @hpd_cb: Hot plug detection callback, registered with
> > > +    * drm_bridge_hpd_enable().
> > > +    */
> > > +   void (*hpd_cb)(void *data, enum drm_connector_status status);
> > > +   /**
> > > +    * @hpd_data: Private data passed to the Hot plug detection callback
> > > +    * @hpd_cb.
> > > +    */
> > > +   void *hpd_data;
> > >  };
> > >
> > >  static inline struct drm_bridge *
> > > @@ -660,6 +837,19 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
> > >                                     u32 output_fmt,
> > >                                     unsigned int *num_input_fmts);
> > >
> > > +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
> > > +int drm_bridge_get_modes(struct drm_bridge *bridge,
> > > +                    struct drm_connector *connector);
> > > +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> > > +                            struct drm_connector *connector);
> > > +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > > +                      void (*cb)(void *data,
> > > +                                 enum drm_connector_status status),
> > > +                      void *data);
> > > +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
> > > +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > > +                      enum drm_connector_status status);
> > > +
> > >  #ifdef CONFIG_DRM_PANEL_BRIDGE
> > >  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
> > >  struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,
>
> --
> Regards,
>
> Laurent Pinchart
Laurent Pinchart Feb. 21, 2020, 2:23 p.m. UTC | #4
Hi Daniel,

On Tue, Feb 18, 2020 at 07:44:19AM +0100, Daniel Vetter wrote:
> On Tue, Feb 18, 2020 at 2:21 AM Laurent Pinchart wrote:
> > On Mon, Feb 17, 2020 at 10:53:08AM +0100, Daniel Vetter wrote:
> >> On Sun, Feb 16, 2020 at 11:02:21PM +0200, Laurent Pinchart wrote:
> >>> To support implementation of DRM connectors on top of DRM bridges
> >>> instead of by bridges, the drm_bridge needs to expose new operations and
> >>> data:
> >>>
> >>> - Output detection, hot-plug notification, mode retrieval and EDID
> >>>   retrieval operations
> >>> - Bitmask of supported operations
> >>> - Bridge output type
> >>> - I2C adapter for DDC access
> >>>
> >>> Add and document these.
> >>>
> >>> Three new bridge helper functions are also added to handle hot plug
> >>> notification in a way that is as transparent as possible for the
> >>> bridges.
> >>>
> >>> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >>> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> >>> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
> >>> ---
> >>> Changes since v3:
> >>>
> >>> - Fix typos
> >>>
> >>> Changes since v2:
> >>>
> >>> - Add wrappers around the .detect(), .get_modes() and .get_edid()
> >>>   operations
> >>> - Warn bridge drivers about valid usage of the connector argument to
> >>>   .get_modes() and .get_edid()
> >>>
> >>> Changes since v1:
> >>>
> >>> - Make .hpd_enable() and .hpd_disable() optional
> >>> - Rename .lost_hotplug() to .hpd_notify()
> >>> - Add ddc field to drm_bridge
> >>> ---
> >>>  drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++
> >>>  include/drm/drm_bridge.h     | 192 ++++++++++++++++++++++++++++++++++-
> >>>  2 files changed, 353 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> >>> index 68ab933ee430..78d26a9a3ee6 100644
> >>> --- a/drivers/gpu/drm/drm_bridge.c
> >>> +++ b/drivers/gpu/drm/drm_bridge.c
> >>> @@ -71,6 +71,8 @@ static LIST_HEAD(bridge_list);
> >>>   */
> >>>  void drm_bridge_add(struct drm_bridge *bridge)
> >>>  {
> >>> +   mutex_init(&bridge->hpd_mutex);
> >>> +
> >>>     mutex_lock(&bridge_lock);
> >>>     list_add_tail(&bridge->list, &bridge_list);
> >>>     mutex_unlock(&bridge_lock);
> >>> @@ -87,6 +89,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
> >>>     mutex_lock(&bridge_lock);
> >>>     list_del_init(&bridge->list);
> >>>     mutex_unlock(&bridge_lock);
> >>> +
> >>> +   mutex_destroy(&bridge->hpd_mutex);
> >>>  }
> >>>  EXPORT_SYMBOL(drm_bridge_remove);
> >>>
> >>> @@ -919,6 +923,164 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
> >>>  }
> >>>  EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
> >>>
> >>> +/**
> >>> + * drm_bridge_detect - check if anything is attached to the bridge output
> >>> + * @bridge: bridge control structure
> >>> + *
> >>> + * If the bridge supports output detection, as reported by the
> >>> + * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
> >>> + * bridge and return the connection status. Otherwise return
> >>> + * connector_status_unknown.
> >>> + *
> >>> + * RETURNS:
> >>> + * The detection status on success, or connector_status_unknown if the bridge
> >>> + * doesn't support output detection.
> >>> + */
> >>> +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge)
> >>> +{
> >>> +   if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
> >>> +           return connector_status_unknown;
> >>> +
> >>> +   return bridge->funcs->detect(bridge);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(drm_bridge_detect);
> >>> +
> >>> +/**
> >>> + * drm_bridge_get_modes - fill all modes currently valid for the sink into the
> >>> + * @connector
> >>> + * @bridge: bridge control structure
> >>> + * @connector: the connector to fill with modes
> >>> + *
> >>> + * If the bridge supports output modes retrieval, as reported by the
> >>> + * DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
> >>> + * fill the connector with all valid modes and return the number of modes
> >>> + * added. Otherwise return 0.
> >>> + *
> >>> + * RETURNS:
> >>> + * The number of modes added to the connector.
> >>> + */
> >>> +int drm_bridge_get_modes(struct drm_bridge *bridge,
> >>> +                    struct drm_connector *connector)
> >>> +{
> >>> +   if (!(bridge->ops & DRM_BRIDGE_OP_MODES))
> >>> +           return 0;
> >>> +
> >>> +   return bridge->funcs->get_modes(bridge, connector);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(drm_bridge_get_modes);
> >>> +
> >>> +/**
> >>> + * drm_bridge_get_edid - get the EDID data of the connected display
> >>> + * @bridge: bridge control structure
> >>> + * @connector: the connector to read EDID for
> >>> + *
> >>> + * If the bridge supports output EDID retrieval, as reported by the
> >>> + * DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
> >>> + * get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
> >>> + *
> >>> + * RETURNS:
> >>> + * The retrieved EDID on success, or an error pointer otherwise.
> >>> + */
> >>> +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> >>> +                            struct drm_connector *connector)
> >>> +{
> >>> +   if (!(bridge->ops & DRM_BRIDGE_OP_EDID))
> >>> +           return ERR_PTR(-ENOTSUPP);
> >>> +
> >>> +   return bridge->funcs->get_edid(bridge, connector);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(drm_bridge_get_edid);
> >>> +
> >>> +/**
> >>> + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
> >>> + * @bridge: bridge control structure
> >>> + * @cb: hot-plug detection callback
> >>> + * @data: data to be passed to the hot-plug detection callback
> >>> + *
> >>> + * Call &drm_bridge_funcs.hpd_enable if implemented and register the given @cb
> >>> + * and @data as hot plug notification callback. From now on the @cb will be
> >>> + * called with @data when an output status change is detected by the bridge,
> >>> + * until hot plug notification gets disabled with drm_bridge_hpd_disable().
> >>> + *
> >>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> >>> + * bridge->ops. This function shall not be called when the flag is not set.
> >>> + *
> >>> + * Only one hot plug detection callback can be registered at a time, it is an
> >>> + * error to call this function when hot plug detection is already enabled for
> >>> + * the bridge.
> >>> + */
> >>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> >>> +                      void (*cb)(void *data,
> >>> +                                 enum drm_connector_status status),
> >>> +                      void *data)
> >>> +{
> >>> +   if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> >>
> >> Supplying a NULL bridge is a caller bug imo, and you're inconsistent in
> >> handling this. Imo just drop.
> >
> > Sounds good to me, I'll drop it.
> >
> >>> +           return;
> >>> +
> >>> +   mutex_lock(&bridge->hpd_mutex);
> >>> +
> >>> +   if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
> >>> +           goto unlock;
> >>> +
> >>> +   bridge->hpd_cb = cb;
> >>> +   bridge->hpd_data = data;
> >>> +
> >>> +   if (bridge->funcs->hpd_enable)
> >>> +           bridge->funcs->hpd_enable(bridge);
> >>> +
> >>> +unlock:
> >>> +   mutex_unlock(&bridge->hpd_mutex);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
> >>> +
> >>> +/**
> >>> + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
> >>> + * @bridge: bridge control structure
> >>> + *
> >>> + * Call &drm_bridge_funcs.hpd_disable if implemented and unregister the hot
> >>> + * plug detection callback previously registered with drm_bridge_hpd_enable().
> >>> + * Once this function returns the callback will not be called by the bridge
> >>> + * when an output status change occurs.
> >>> + *
> >>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> >>> + * bridge->ops. This function shall not be called when the flag is not set.
> >>> + */
> >>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
> >>> +{
> >>> +   if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> >>> +           return;
> >>> +
> >>> +   mutex_lock(&bridge->hpd_mutex);
> >>> +   if (bridge->funcs->hpd_disable)
> >>> +           bridge->funcs->hpd_disable(bridge);
> >>> +
> >>> +   bridge->hpd_cb = NULL;
> >>> +   bridge->hpd_data = NULL;
> >>> +   mutex_unlock(&bridge->hpd_mutex);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
> >>> +
> >>> +/**
> >>> + * drm_bridge_hpd_notify - notify hot plug detection events
> >>> + * @bridge: bridge control structure
> >>> + * @status: output connection status
> >>> + *
> >>> + * Bridge drivers shall call this function to report hot plug events when they
> >>> + * detect a change in the output status, when hot plug detection has been
> >>> + * enabled by drm_bridge_hpd_enable().
> >>> + *
> >>> + * This function shall be called in a context that can sleep.
> >>> + */
> >>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> >>> +                      enum drm_connector_status status)
> >>> +{
> >>> +   mutex_lock(&bridge->hpd_mutex);
> >>> +   if (bridge->hpd_cb)
> >>> +           bridge->hpd_cb(bridge->hpd_data, status);
> >>> +   mutex_unlock(&bridge->hpd_mutex);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
> >>> +
> >>>  #ifdef CONFIG_OF
> >>>  /**
> >>>   * of_drm_find_bridge - find the bridge corresponding to the device node in
> >>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> >>> index 45626ecf20f8..ba9b7c84f11e 100644
> >>> --- a/include/drm/drm_bridge.h
> >>> +++ b/include/drm/drm_bridge.h
> >>> @@ -23,8 +23,9 @@
> >>>  #ifndef __DRM_BRIDGE_H__
> >>>  #define __DRM_BRIDGE_H__
> >>>
> >>> -#include <linux/list.h>
> >>>  #include <linux/ctype.h>
> >>> +#include <linux/list.h>
> >>> +#include <linux/mutex.h>
> >>>
> >>>  #include <drm/drm_atomic.h>
> >>>  #include <drm/drm_encoder.h>
> >>> @@ -33,7 +34,10 @@
> >>>
> >>>  struct drm_bridge;
> >>>  struct drm_bridge_timings;
> >>> +struct drm_connector;
> >>>  struct drm_panel;
> >>> +struct edid;
> >>> +struct i2c_adapter;
> >>>
> >>>  /**
> >>>   * struct drm_bridge_funcs - drm_bridge control functions
> >>> @@ -488,6 +492,119 @@ struct drm_bridge_funcs {
> >>>      * giving the reason of the failure otherwise.
> >>>      */
> >>>     struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
> >>> +
> >>> +   /**
> >>> +    * @detect:
> >>> +    *
> >>> +    * Check if anything is attached to the bridge output.
> >>> +    *
> >>> +    * This callback is optional, if not implemented the bridge will be
> >>> +    * considered as always having a component attached to its output.
> >>> +    * Bridges that implement this callback shall set the
> >>> +    * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
> >>> +    *
> >>> +    * RETURNS:
> >>> +    *
> >>> +    * drm_connector_status indicating the bridge output status.
> >>> +    */
> >>> +   enum drm_connector_status (*detect)(struct drm_bridge *bridge);
> >>> +
> >>> +   /**
> >>> +    * @get_modes:
> >>> +    *
> >>> +    * Fill all modes currently valid for the sink into the &drm_connector
> >>> +    * with drm_mode_probed_add().
> >>> +    *
> >>> +    * The @get_modes callback is mostly intended to support non-probeable
> >>> +    * displays such as many fixed panels. Bridges that support reading
> >>> +    * EDID shall leave @get_modes unimplemented and implement the
> >>> +    * &drm_bridge_funcs->get_edid callback instead.
> >>> +    *
> >>> +    * This callback is optional. Bridges that implement it shall set the
> >>> +    * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
> >>> +    *
> >>> +    * The connector parameter shall be used for the sole purpose of
> >>> +    * filling modes, and shall not be stored internally by bridge drivers
> >>> +    * for future usage.
> >>> +    *
> >>> +    * RETURNS:
> >>> +    *
> >>> +    * The number of modes added by calling drm_mode_probed_add().
> >>> +    */
> >>> +   int (*get_modes)(struct drm_bridge *bridge,
> >>> +                    struct drm_connector *connector);
> >>> +
> >>> +   /**
> >>> +    * @get_edid:
> >>> +    *
> >>> +    * Read and parse the EDID data of the connected display.
> >>> +    *
> >>> +    * The @get_edid callback is the preferred way of reporting mode
> >>> +    * information for a display connected to the bridge output. Bridges
> >>> +    * that support reading EDID shall implement this callback and leave
> >>> +    * the @get_modes callback unimplemented.
> >>> +    *
> >>> +    * The caller of this operation shall first verify the output
> >>> +    * connection status and refrain from reading EDID from a disconnected
> >>> +    * output.
> >>> +    *
> >>> +    * This callback is optional. Bridges that implement it shall set the
> >>> +    * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
> >>> +    *
> >>> +    * The connector parameter shall be used for the sole purpose of EDID
> >>> +    * retrieval and parsing, and shall not be stored internally by bridge
> >>> +    * drivers for future usage.
> >>> +    *
> >>> +    * RETURNS:
> >>> +    *
> >>> +    * An edid structure newly allocated with kmalloc() (or similar) on
> >>> +    * success, or NULL otherwise. The caller is responsible for freeing
> >>> +    * the returned edid structure with kfree().
> >>> +    */
> >>> +   struct edid *(*get_edid)(struct drm_bridge *bridge,
> >>> +                            struct drm_connector *connector);
> >>> +
> >>> +   /**
> >>> +    * @hpd_notify:
> >>> +    *
> >>> +    * Notify the bridge of hot plug detection.
> >>> +    *
> >>> +    * This callback is optional, it may be implemented by bridges that
> >>> +    * need to be notified of display connection or disconnection for
> >>> +    * internal reasons. One use case is to reset the internal state of CEC
> >>> +    * controllers for HDMI bridges.
> >>> +    */
> >>> +   void (*hpd_notify)(struct drm_bridge *bridge,
> >>> +                      enum drm_connector_status status);
> >>> +
> >>> +   /**
> >>> +    * @hpd_enable:
> >>> +    *
> >>> +    * Enable hot plug detection. From now on the bridge shall call
> >>> +    * drm_bridge_hpd_notify() each time a change is detected in the output
> >>> +    * connection status, until hot plug detection gets disabled with
> >>> +    * @hpd_disable.
> >>> +    *
> >>> +    * This callback is optional and shall only be implemented by bridges
> >>> +    * that support hot-plug notification without polling. Bridges that
> >>> +    * implement it shall also implement the @hpd_disable callback and set
> >>> +    * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> >>> +    */
> >>> +   void (*hpd_enable)(struct drm_bridge *bridge);
> >>> +
> >>> +   /**
> >>> +    * @hpd_disable:
> >>> +    *
> >>> +    * Disable hot plug detection. Once this function returns the bridge
> >>> +    * shall not call drm_bridge_hpd_notify() when a change in the output
> >>> +    * connection status occurs.
> >>> +    *
> >>> +    * This callback is optional and shall only be implemented by bridges
> >>> +    * that support hot-plug notification without polling. Bridges that
> >>> +    * implement it shall also implement the @hpd_enable callback and set
> >>> +    * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> >>> +    */
> >>> +   void (*hpd_disable)(struct drm_bridge *bridge);
> >>>  };
> >>>
> >>>  /**
> >>> @@ -526,6 +643,39 @@ struct drm_bridge_timings {
> >>>     bool dual_link;
> >>>  };
> >>>
> >>> +/**
> >>> + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
> >>> + */
> >>> +enum drm_bridge_ops {
> >>> +   /**
> >>> +    * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
> >>> +    * its output. Bridges that set this flag shall implement the
> >>> +    * &drm_bridge_funcs->detect callback.
> >>> +    */
> >>> +   DRM_BRIDGE_OP_DETECT = BIT(0),
> >>> +   /**
> >>> +    * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
> >>> +    * connected to its output. Bridges that set this flag shall implement
> >>> +    * the &drm_bridge_funcs->get_edid callback.
> >>> +    */
> >>> +   DRM_BRIDGE_OP_EDID = BIT(1),
> >>> +   /**
> >>> +    * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
> >>> +    * without requiring polling. Bridges that set this flag shall
> >>> +    * implement the &drm_bridge_funcs->hpd_enable and
> >>> +    * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
> >>> +    * and disabling hot-plug detection dynamically.
> >>> +    */
> >>> +   DRM_BRIDGE_OP_HPD = BIT(2),
> >>> +   /**
> >>> +    * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
> >>> +    * by the display at its output. This does not include reading EDID
> >>> +    * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
> >>> +    * this flag shall implement the &drm_bridge_funcs->get_modes callback.
> >>> +    */
> >>> +   DRM_BRIDGE_OP_MODES = BIT(3),
> >>> +};
> >>
> >> I still don't like this one here, since most of them are tracking
> >> redundant information. If you don't like just checking for the hook
> >> directly wrap it in a helper, e.g.
> >>
> >> bool drm_bridge_supports_detect(bridge)
> >> {
> >>       return bridge->ops->detect;
> >> }
> >
> > It seems I've done a really bad job explaining why the flags are
> > required, so let me try again :-)
> >
> > There's a difference between supporting an operation in a driver, and
> > supporting it in a given system. When a bridge hardware supports reading
> > EDID, or detecting hotplug, the driver will implement this and expose
> > the corresponding operation in drm_bridge_funcs by setting the function
> > pointers appropriately.
> >
> > However, this doesn't mean that the DDC lines are wired to the bridge on
> > a particular board, they could be connected to an I2C controller of the
> > SoC. Same for the HPD line, it could be connected to a GPIO instead of a
> > dedicated pin of the bridge. This board-specific information is reported
> > by the firmware (ACPI or DT), parsed by the bridge driver, and reflected
> > in the drm_bridge_ops flags.
> >
> > drm_bridge_funcs and drm_bridge_ops are thus different, the latter
> > supplements the former. We could merge the two by setting the
> > corresponding function pointer in drm_bridge_funcs to NULL when the
> > drm_bridge_ops flag isn't set. This would however require allocating
> > drm_bridge_funcs dynamically (either by embedding it into a
> > driver-specific structure, or allocating it dynamically directly)
> > instead of using a global static const struct, and this is considered to
> > be a security issue as it allows a potential attacker to overwrite
> > function pointers (there have been quite a lot of security patches
> > merged that move function pointers to .rodata or otherwise const
> > memory).
> 
> Hm so I'm pretty sure you've explained this to me already (at least!)
> once in the past, and your favorite context-free & stateless reviewer
> didn't bother to remember :-)
> 
> I think it's time to improve the intro DOC: section with a few special
> notes on chaining bridges. That didn't happen ever since the original
> bridge stuff landed, and that non-working idea from years ago evolved
> a lot with all this work now. I think adding an entire sub-section or
> separate DOC comment for this, which maybe also links to the
> connector-bridge helper and kinda ties the entire story you guys
> developed together would be really good. Otherwise I'm pretty sure
> this is not going to be the last time you have to explain this to
> someone ...

Why ô why did I have to start the DRM/KMS documentation effort years
ago, to see it biting me back now ? :-)

I'll give it a go. It may not cover the whole bridge API though,
depending on how much time I can spend, but will definitely cover this
and put it in context.

> >> hpd seems to be special, since a bridge can support hotplug but not have
> >> the enable_hpd/disable_hpd hooks. Which smells somewhat fishy, since if
> >> you have multiple bridges with hpd, how do you make sure you get hpd
> >> events only from the right one?
> >
> > On a given board HPD should only be generated by one bridge in practice.
> > If we ever encounter systems where multiple bridges can generate HPD for
> > the same external HPD event, I think we can deal with them at that time.
> >
> >> Aside from that just having a
> >>
> >>       bool supports_hpd;
> >>
> >> seems a lot simpler.
> >
> > If we only needed DRM_BRIDGE_OP_HPD, I agree that a bool would be
> > simpler, but as explained above we need the other ones too :-)
> >
> >> Yes I know that the drm DRIVER_FOO flags don't work like that, and I'm
> >> kinda unhappy about them since forever. Managed to delete most of them
> >> even :-)
> >>
> >>> +
> >>>  /**
> >>>   * struct drm_bridge - central DRM bridge control structure
> >>>   */
> >>> @@ -554,6 +704,33 @@ struct drm_bridge {
> >>>     const struct drm_bridge_funcs *funcs;
> >>>     /** @driver_private: pointer to the bridge driver's internal context */
> >>>     void *driver_private;
> >>> +   /** @ops: bitmask of operations supported by the bridge */
> >>> +   enum drm_bridge_ops ops;
> >>> +   /**
> >>> +    * @type: Type of the connection at the bridge output
> >>> +    * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
> >>> +    * identifies the type of connected display.
> >>> +    */
> >>> +   int type;
> >>> +   /**
> >>> +    * @ddc: Associated I2C adapter for DDC access, if any.
> >>> +    */
> >>> +   struct i2c_adapter *ddc;
> >>> +   /** private: */
> >>> +   /**
> >>> +    * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
> >>> +    */
> >>> +   struct mutex hpd_mutex;
> >>> +   /**
> >>> +    * @hpd_cb: Hot plug detection callback, registered with
> >>> +    * drm_bridge_hpd_enable().
> >>> +    */
> >>> +   void (*hpd_cb)(void *data, enum drm_connector_status status);
> >>> +   /**
> >>> +    * @hpd_data: Private data passed to the Hot plug detection callback
> >>> +    * @hpd_cb.
> >>> +    */
> >>> +   void *hpd_data;
> >>>  };
> >>>
> >>>  static inline struct drm_bridge *
> >>> @@ -660,6 +837,19 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
> >>>                                     u32 output_fmt,
> >>>                                     unsigned int *num_input_fmts);
> >>>
> >>> +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
> >>> +int drm_bridge_get_modes(struct drm_bridge *bridge,
> >>> +                    struct drm_connector *connector);
> >>> +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> >>> +                            struct drm_connector *connector);
> >>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> >>> +                      void (*cb)(void *data,
> >>> +                                 enum drm_connector_status status),
> >>> +                      void *data);
> >>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
> >>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> >>> +                      enum drm_connector_status status);
> >>> +
> >>>  #ifdef CONFIG_DRM_PANEL_BRIDGE
> >>>  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
> >>>  struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,
Daniel Vetter Feb. 21, 2020, 5:05 p.m. UTC | #5
On Fri, Feb 21, 2020 at 04:23:24PM +0200, Laurent Pinchart wrote:
> Hi Daniel,
> 
> On Tue, Feb 18, 2020 at 07:44:19AM +0100, Daniel Vetter wrote:
> > On Tue, Feb 18, 2020 at 2:21 AM Laurent Pinchart wrote:
> > > On Mon, Feb 17, 2020 at 10:53:08AM +0100, Daniel Vetter wrote:
> > >> On Sun, Feb 16, 2020 at 11:02:21PM +0200, Laurent Pinchart wrote:
> > >>> To support implementation of DRM connectors on top of DRM bridges
> > >>> instead of by bridges, the drm_bridge needs to expose new operations and
> > >>> data:
> > >>>
> > >>> - Output detection, hot-plug notification, mode retrieval and EDID
> > >>>   retrieval operations
> > >>> - Bitmask of supported operations
> > >>> - Bridge output type
> > >>> - I2C adapter for DDC access
> > >>>
> > >>> Add and document these.
> > >>>
> > >>> Three new bridge helper functions are also added to handle hot plug
> > >>> notification in a way that is as transparent as possible for the
> > >>> bridges.
> > >>>
> > >>> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > >>> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > >>> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
> > >>> ---
> > >>> Changes since v3:
> > >>>
> > >>> - Fix typos
> > >>>
> > >>> Changes since v2:
> > >>>
> > >>> - Add wrappers around the .detect(), .get_modes() and .get_edid()
> > >>>   operations
> > >>> - Warn bridge drivers about valid usage of the connector argument to
> > >>>   .get_modes() and .get_edid()
> > >>>
> > >>> Changes since v1:
> > >>>
> > >>> - Make .hpd_enable() and .hpd_disable() optional
> > >>> - Rename .lost_hotplug() to .hpd_notify()
> > >>> - Add ddc field to drm_bridge
> > >>> ---
> > >>>  drivers/gpu/drm/drm_bridge.c | 162 +++++++++++++++++++++++++++++
> > >>>  include/drm/drm_bridge.h     | 192 ++++++++++++++++++++++++++++++++++-
> > >>>  2 files changed, 353 insertions(+), 1 deletion(-)
> > >>>
> > >>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > >>> index 68ab933ee430..78d26a9a3ee6 100644
> > >>> --- a/drivers/gpu/drm/drm_bridge.c
> > >>> +++ b/drivers/gpu/drm/drm_bridge.c
> > >>> @@ -71,6 +71,8 @@ static LIST_HEAD(bridge_list);
> > >>>   */
> > >>>  void drm_bridge_add(struct drm_bridge *bridge)
> > >>>  {
> > >>> +   mutex_init(&bridge->hpd_mutex);
> > >>> +
> > >>>     mutex_lock(&bridge_lock);
> > >>>     list_add_tail(&bridge->list, &bridge_list);
> > >>>     mutex_unlock(&bridge_lock);
> > >>> @@ -87,6 +89,8 @@ void drm_bridge_remove(struct drm_bridge *bridge)
> > >>>     mutex_lock(&bridge_lock);
> > >>>     list_del_init(&bridge->list);
> > >>>     mutex_unlock(&bridge_lock);
> > >>> +
> > >>> +   mutex_destroy(&bridge->hpd_mutex);
> > >>>  }
> > >>>  EXPORT_SYMBOL(drm_bridge_remove);
> > >>>
> > >>> @@ -919,6 +923,164 @@ int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
> > >>>  }
> > >>>  EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
> > >>>
> > >>> +/**
> > >>> + * drm_bridge_detect - check if anything is attached to the bridge output
> > >>> + * @bridge: bridge control structure
> > >>> + *
> > >>> + * If the bridge supports output detection, as reported by the
> > >>> + * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
> > >>> + * bridge and return the connection status. Otherwise return
> > >>> + * connector_status_unknown.
> > >>> + *
> > >>> + * RETURNS:
> > >>> + * The detection status on success, or connector_status_unknown if the bridge
> > >>> + * doesn't support output detection.
> > >>> + */
> > >>> +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge)
> > >>> +{
> > >>> +   if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
> > >>> +           return connector_status_unknown;
> > >>> +
> > >>> +   return bridge->funcs->detect(bridge);
> > >>> +}
> > >>> +EXPORT_SYMBOL_GPL(drm_bridge_detect);
> > >>> +
> > >>> +/**
> > >>> + * drm_bridge_get_modes - fill all modes currently valid for the sink into the
> > >>> + * @connector
> > >>> + * @bridge: bridge control structure
> > >>> + * @connector: the connector to fill with modes
> > >>> + *
> > >>> + * If the bridge supports output modes retrieval, as reported by the
> > >>> + * DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
> > >>> + * fill the connector with all valid modes and return the number of modes
> > >>> + * added. Otherwise return 0.
> > >>> + *
> > >>> + * RETURNS:
> > >>> + * The number of modes added to the connector.
> > >>> + */
> > >>> +int drm_bridge_get_modes(struct drm_bridge *bridge,
> > >>> +                    struct drm_connector *connector)
> > >>> +{
> > >>> +   if (!(bridge->ops & DRM_BRIDGE_OP_MODES))
> > >>> +           return 0;
> > >>> +
> > >>> +   return bridge->funcs->get_modes(bridge, connector);
> > >>> +}
> > >>> +EXPORT_SYMBOL_GPL(drm_bridge_get_modes);
> > >>> +
> > >>> +/**
> > >>> + * drm_bridge_get_edid - get the EDID data of the connected display
> > >>> + * @bridge: bridge control structure
> > >>> + * @connector: the connector to read EDID for
> > >>> + *
> > >>> + * If the bridge supports output EDID retrieval, as reported by the
> > >>> + * DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
> > >>> + * get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
> > >>> + *
> > >>> + * RETURNS:
> > >>> + * The retrieved EDID on success, or an error pointer otherwise.
> > >>> + */
> > >>> +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> > >>> +                            struct drm_connector *connector)
> > >>> +{
> > >>> +   if (!(bridge->ops & DRM_BRIDGE_OP_EDID))
> > >>> +           return ERR_PTR(-ENOTSUPP);
> > >>> +
> > >>> +   return bridge->funcs->get_edid(bridge, connector);
> > >>> +}
> > >>> +EXPORT_SYMBOL_GPL(drm_bridge_get_edid);
> > >>> +
> > >>> +/**
> > >>> + * drm_bridge_hpd_enable - enable hot plug detection for the bridge
> > >>> + * @bridge: bridge control structure
> > >>> + * @cb: hot-plug detection callback
> > >>> + * @data: data to be passed to the hot-plug detection callback
> > >>> + *
> > >>> + * Call &drm_bridge_funcs.hpd_enable if implemented and register the given @cb
> > >>> + * and @data as hot plug notification callback. From now on the @cb will be
> > >>> + * called with @data when an output status change is detected by the bridge,
> > >>> + * until hot plug notification gets disabled with drm_bridge_hpd_disable().
> > >>> + *
> > >>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> > >>> + * bridge->ops. This function shall not be called when the flag is not set.
> > >>> + *
> > >>> + * Only one hot plug detection callback can be registered at a time, it is an
> > >>> + * error to call this function when hot plug detection is already enabled for
> > >>> + * the bridge.
> > >>> + */
> > >>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > >>> +                      void (*cb)(void *data,
> > >>> +                                 enum drm_connector_status status),
> > >>> +                      void *data)
> > >>> +{
> > >>> +   if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> > >>
> > >> Supplying a NULL bridge is a caller bug imo, and you're inconsistent in
> > >> handling this. Imo just drop.
> > >
> > > Sounds good to me, I'll drop it.
> > >
> > >>> +           return;
> > >>> +
> > >>> +   mutex_lock(&bridge->hpd_mutex);
> > >>> +
> > >>> +   if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
> > >>> +           goto unlock;
> > >>> +
> > >>> +   bridge->hpd_cb = cb;
> > >>> +   bridge->hpd_data = data;
> > >>> +
> > >>> +   if (bridge->funcs->hpd_enable)
> > >>> +           bridge->funcs->hpd_enable(bridge);
> > >>> +
> > >>> +unlock:
> > >>> +   mutex_unlock(&bridge->hpd_mutex);
> > >>> +}
> > >>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
> > >>> +
> > >>> +/**
> > >>> + * drm_bridge_hpd_disable - disable hot plug detection for the bridge
> > >>> + * @bridge: bridge control structure
> > >>> + *
> > >>> + * Call &drm_bridge_funcs.hpd_disable if implemented and unregister the hot
> > >>> + * plug detection callback previously registered with drm_bridge_hpd_enable().
> > >>> + * Once this function returns the callback will not be called by the bridge
> > >>> + * when an output status change occurs.
> > >>> + *
> > >>> + * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
> > >>> + * bridge->ops. This function shall not be called when the flag is not set.
> > >>> + */
> > >>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge)
> > >>> +{
> > >>> +   if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
> > >>> +           return;
> > >>> +
> > >>> +   mutex_lock(&bridge->hpd_mutex);
> > >>> +   if (bridge->funcs->hpd_disable)
> > >>> +           bridge->funcs->hpd_disable(bridge);
> > >>> +
> > >>> +   bridge->hpd_cb = NULL;
> > >>> +   bridge->hpd_data = NULL;
> > >>> +   mutex_unlock(&bridge->hpd_mutex);
> > >>> +}
> > >>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
> > >>> +
> > >>> +/**
> > >>> + * drm_bridge_hpd_notify - notify hot plug detection events
> > >>> + * @bridge: bridge control structure
> > >>> + * @status: output connection status
> > >>> + *
> > >>> + * Bridge drivers shall call this function to report hot plug events when they
> > >>> + * detect a change in the output status, when hot plug detection has been
> > >>> + * enabled by drm_bridge_hpd_enable().
> > >>> + *
> > >>> + * This function shall be called in a context that can sleep.
> > >>> + */
> > >>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > >>> +                      enum drm_connector_status status)
> > >>> +{
> > >>> +   mutex_lock(&bridge->hpd_mutex);
> > >>> +   if (bridge->hpd_cb)
> > >>> +           bridge->hpd_cb(bridge->hpd_data, status);
> > >>> +   mutex_unlock(&bridge->hpd_mutex);
> > >>> +}
> > >>> +EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
> > >>> +
> > >>>  #ifdef CONFIG_OF
> > >>>  /**
> > >>>   * of_drm_find_bridge - find the bridge corresponding to the device node in
> > >>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> > >>> index 45626ecf20f8..ba9b7c84f11e 100644
> > >>> --- a/include/drm/drm_bridge.h
> > >>> +++ b/include/drm/drm_bridge.h
> > >>> @@ -23,8 +23,9 @@
> > >>>  #ifndef __DRM_BRIDGE_H__
> > >>>  #define __DRM_BRIDGE_H__
> > >>>
> > >>> -#include <linux/list.h>
> > >>>  #include <linux/ctype.h>
> > >>> +#include <linux/list.h>
> > >>> +#include <linux/mutex.h>
> > >>>
> > >>>  #include <drm/drm_atomic.h>
> > >>>  #include <drm/drm_encoder.h>
> > >>> @@ -33,7 +34,10 @@
> > >>>
> > >>>  struct drm_bridge;
> > >>>  struct drm_bridge_timings;
> > >>> +struct drm_connector;
> > >>>  struct drm_panel;
> > >>> +struct edid;
> > >>> +struct i2c_adapter;
> > >>>
> > >>>  /**
> > >>>   * struct drm_bridge_funcs - drm_bridge control functions
> > >>> @@ -488,6 +492,119 @@ struct drm_bridge_funcs {
> > >>>      * giving the reason of the failure otherwise.
> > >>>      */
> > >>>     struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
> > >>> +
> > >>> +   /**
> > >>> +    * @detect:
> > >>> +    *
> > >>> +    * Check if anything is attached to the bridge output.
> > >>> +    *
> > >>> +    * This callback is optional, if not implemented the bridge will be
> > >>> +    * considered as always having a component attached to its output.
> > >>> +    * Bridges that implement this callback shall set the
> > >>> +    * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
> > >>> +    *
> > >>> +    * RETURNS:
> > >>> +    *
> > >>> +    * drm_connector_status indicating the bridge output status.
> > >>> +    */
> > >>> +   enum drm_connector_status (*detect)(struct drm_bridge *bridge);
> > >>> +
> > >>> +   /**
> > >>> +    * @get_modes:
> > >>> +    *
> > >>> +    * Fill all modes currently valid for the sink into the &drm_connector
> > >>> +    * with drm_mode_probed_add().
> > >>> +    *
> > >>> +    * The @get_modes callback is mostly intended to support non-probeable
> > >>> +    * displays such as many fixed panels. Bridges that support reading
> > >>> +    * EDID shall leave @get_modes unimplemented and implement the
> > >>> +    * &drm_bridge_funcs->get_edid callback instead.
> > >>> +    *
> > >>> +    * This callback is optional. Bridges that implement it shall set the
> > >>> +    * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
> > >>> +    *
> > >>> +    * The connector parameter shall be used for the sole purpose of
> > >>> +    * filling modes, and shall not be stored internally by bridge drivers
> > >>> +    * for future usage.
> > >>> +    *
> > >>> +    * RETURNS:
> > >>> +    *
> > >>> +    * The number of modes added by calling drm_mode_probed_add().
> > >>> +    */
> > >>> +   int (*get_modes)(struct drm_bridge *bridge,
> > >>> +                    struct drm_connector *connector);
> > >>> +
> > >>> +   /**
> > >>> +    * @get_edid:
> > >>> +    *
> > >>> +    * Read and parse the EDID data of the connected display.
> > >>> +    *
> > >>> +    * The @get_edid callback is the preferred way of reporting mode
> > >>> +    * information for a display connected to the bridge output. Bridges
> > >>> +    * that support reading EDID shall implement this callback and leave
> > >>> +    * the @get_modes callback unimplemented.
> > >>> +    *
> > >>> +    * The caller of this operation shall first verify the output
> > >>> +    * connection status and refrain from reading EDID from a disconnected
> > >>> +    * output.
> > >>> +    *
> > >>> +    * This callback is optional. Bridges that implement it shall set the
> > >>> +    * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
> > >>> +    *
> > >>> +    * The connector parameter shall be used for the sole purpose of EDID
> > >>> +    * retrieval and parsing, and shall not be stored internally by bridge
> > >>> +    * drivers for future usage.
> > >>> +    *
> > >>> +    * RETURNS:
> > >>> +    *
> > >>> +    * An edid structure newly allocated with kmalloc() (or similar) on
> > >>> +    * success, or NULL otherwise. The caller is responsible for freeing
> > >>> +    * the returned edid structure with kfree().
> > >>> +    */
> > >>> +   struct edid *(*get_edid)(struct drm_bridge *bridge,
> > >>> +                            struct drm_connector *connector);
> > >>> +
> > >>> +   /**
> > >>> +    * @hpd_notify:
> > >>> +    *
> > >>> +    * Notify the bridge of hot plug detection.
> > >>> +    *
> > >>> +    * This callback is optional, it may be implemented by bridges that
> > >>> +    * need to be notified of display connection or disconnection for
> > >>> +    * internal reasons. One use case is to reset the internal state of CEC
> > >>> +    * controllers for HDMI bridges.
> > >>> +    */
> > >>> +   void (*hpd_notify)(struct drm_bridge *bridge,
> > >>> +                      enum drm_connector_status status);
> > >>> +
> > >>> +   /**
> > >>> +    * @hpd_enable:
> > >>> +    *
> > >>> +    * Enable hot plug detection. From now on the bridge shall call
> > >>> +    * drm_bridge_hpd_notify() each time a change is detected in the output
> > >>> +    * connection status, until hot plug detection gets disabled with
> > >>> +    * @hpd_disable.
> > >>> +    *
> > >>> +    * This callback is optional and shall only be implemented by bridges
> > >>> +    * that support hot-plug notification without polling. Bridges that
> > >>> +    * implement it shall also implement the @hpd_disable callback and set
> > >>> +    * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> > >>> +    */
> > >>> +   void (*hpd_enable)(struct drm_bridge *bridge);
> > >>> +
> > >>> +   /**
> > >>> +    * @hpd_disable:
> > >>> +    *
> > >>> +    * Disable hot plug detection. Once this function returns the bridge
> > >>> +    * shall not call drm_bridge_hpd_notify() when a change in the output
> > >>> +    * connection status occurs.
> > >>> +    *
> > >>> +    * This callback is optional and shall only be implemented by bridges
> > >>> +    * that support hot-plug notification without polling. Bridges that
> > >>> +    * implement it shall also implement the @hpd_enable callback and set
> > >>> +    * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
> > >>> +    */
> > >>> +   void (*hpd_disable)(struct drm_bridge *bridge);
> > >>>  };
> > >>>
> > >>>  /**
> > >>> @@ -526,6 +643,39 @@ struct drm_bridge_timings {
> > >>>     bool dual_link;
> > >>>  };
> > >>>
> > >>> +/**
> > >>> + * enum drm_bridge_ops - Bitmask of operations supported by the bridge
> > >>> + */
> > >>> +enum drm_bridge_ops {
> > >>> +   /**
> > >>> +    * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
> > >>> +    * its output. Bridges that set this flag shall implement the
> > >>> +    * &drm_bridge_funcs->detect callback.
> > >>> +    */
> > >>> +   DRM_BRIDGE_OP_DETECT = BIT(0),
> > >>> +   /**
> > >>> +    * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
> > >>> +    * connected to its output. Bridges that set this flag shall implement
> > >>> +    * the &drm_bridge_funcs->get_edid callback.
> > >>> +    */
> > >>> +   DRM_BRIDGE_OP_EDID = BIT(1),
> > >>> +   /**
> > >>> +    * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
> > >>> +    * without requiring polling. Bridges that set this flag shall
> > >>> +    * implement the &drm_bridge_funcs->hpd_enable and
> > >>> +    * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
> > >>> +    * and disabling hot-plug detection dynamically.
> > >>> +    */
> > >>> +   DRM_BRIDGE_OP_HPD = BIT(2),
> > >>> +   /**
> > >>> +    * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
> > >>> +    * by the display at its output. This does not include reading EDID
> > >>> +    * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
> > >>> +    * this flag shall implement the &drm_bridge_funcs->get_modes callback.
> > >>> +    */
> > >>> +   DRM_BRIDGE_OP_MODES = BIT(3),
> > >>> +};
> > >>
> > >> I still don't like this one here, since most of them are tracking
> > >> redundant information. If you don't like just checking for the hook
> > >> directly wrap it in a helper, e.g.
> > >>
> > >> bool drm_bridge_supports_detect(bridge)
> > >> {
> > >>       return bridge->ops->detect;
> > >> }
> > >
> > > It seems I've done a really bad job explaining why the flags are
> > > required, so let me try again :-)
> > >
> > > There's a difference between supporting an operation in a driver, and
> > > supporting it in a given system. When a bridge hardware supports reading
> > > EDID, or detecting hotplug, the driver will implement this and expose
> > > the corresponding operation in drm_bridge_funcs by setting the function
> > > pointers appropriately.
> > >
> > > However, this doesn't mean that the DDC lines are wired to the bridge on
> > > a particular board, they could be connected to an I2C controller of the
> > > SoC. Same for the HPD line, it could be connected to a GPIO instead of a
> > > dedicated pin of the bridge. This board-specific information is reported
> > > by the firmware (ACPI or DT), parsed by the bridge driver, and reflected
> > > in the drm_bridge_ops flags.
> > >
> > > drm_bridge_funcs and drm_bridge_ops are thus different, the latter
> > > supplements the former. We could merge the two by setting the
> > > corresponding function pointer in drm_bridge_funcs to NULL when the
> > > drm_bridge_ops flag isn't set. This would however require allocating
> > > drm_bridge_funcs dynamically (either by embedding it into a
> > > driver-specific structure, or allocating it dynamically directly)
> > > instead of using a global static const struct, and this is considered to
> > > be a security issue as it allows a potential attacker to overwrite
> > > function pointers (there have been quite a lot of security patches
> > > merged that move function pointers to .rodata or otherwise const
> > > memory).
> > 
> > Hm so I'm pretty sure you've explained this to me already (at least!)
> > once in the past, and your favorite context-free & stateless reviewer
> > didn't bother to remember :-)
> > 
> > I think it's time to improve the intro DOC: section with a few special
> > notes on chaining bridges. That didn't happen ever since the original
> > bridge stuff landed, and that non-working idea from years ago evolved
> > a lot with all this work now. I think adding an entire sub-section or
> > separate DOC comment for this, which maybe also links to the
> > connector-bridge helper and kinda ties the entire story you guys
> > developed together would be really good. Otherwise I'm pretty sure
> > this is not going to be the last time you have to explain this to
> > someone ...
> 
> Why ô why did I have to start the DRM/KMS documentation effort years
> ago, to see it biting me back now ? :-)

/me checks the list of nasty documentation slackers ...

You're already on the list for lack of writeback stuff :-P

> I'll give it a go. It may not cover the whole bridge API though,
> depending on how much time I can spend, but will definitely cover this
> and put it in context.

I think just an updated section on chaining and what's the new design
should be good enough, with some pointers to relevant functions. Bonus
points if you can draw a nice diagram for an example :-)

I think the ingredients are all there, so just a few paragraphs at most
(plus nice picture).
-Daniel

> 
> > >> hpd seems to be special, since a bridge can support hotplug but not have
> > >> the enable_hpd/disable_hpd hooks. Which smells somewhat fishy, since if
> > >> you have multiple bridges with hpd, how do you make sure you get hpd
> > >> events only from the right one?
> > >
> > > On a given board HPD should only be generated by one bridge in practice.
> > > If we ever encounter systems where multiple bridges can generate HPD for
> > > the same external HPD event, I think we can deal with them at that time.
> > >
> > >> Aside from that just having a
> > >>
> > >>       bool supports_hpd;
> > >>
> > >> seems a lot simpler.
> > >
> > > If we only needed DRM_BRIDGE_OP_HPD, I agree that a bool would be
> > > simpler, but as explained above we need the other ones too :-)
> > >
> > >> Yes I know that the drm DRIVER_FOO flags don't work like that, and I'm
> > >> kinda unhappy about them since forever. Managed to delete most of them
> > >> even :-)
> > >>
> > >>> +
> > >>>  /**
> > >>>   * struct drm_bridge - central DRM bridge control structure
> > >>>   */
> > >>> @@ -554,6 +704,33 @@ struct drm_bridge {
> > >>>     const struct drm_bridge_funcs *funcs;
> > >>>     /** @driver_private: pointer to the bridge driver's internal context */
> > >>>     void *driver_private;
> > >>> +   /** @ops: bitmask of operations supported by the bridge */
> > >>> +   enum drm_bridge_ops ops;
> > >>> +   /**
> > >>> +    * @type: Type of the connection at the bridge output
> > >>> +    * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
> > >>> +    * identifies the type of connected display.
> > >>> +    */
> > >>> +   int type;
> > >>> +   /**
> > >>> +    * @ddc: Associated I2C adapter for DDC access, if any.
> > >>> +    */
> > >>> +   struct i2c_adapter *ddc;
> > >>> +   /** private: */
> > >>> +   /**
> > >>> +    * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
> > >>> +    */
> > >>> +   struct mutex hpd_mutex;
> > >>> +   /**
> > >>> +    * @hpd_cb: Hot plug detection callback, registered with
> > >>> +    * drm_bridge_hpd_enable().
> > >>> +    */
> > >>> +   void (*hpd_cb)(void *data, enum drm_connector_status status);
> > >>> +   /**
> > >>> +    * @hpd_data: Private data passed to the Hot plug detection callback
> > >>> +    * @hpd_cb.
> > >>> +    */
> > >>> +   void *hpd_data;
> > >>>  };
> > >>>
> > >>>  static inline struct drm_bridge *
> > >>> @@ -660,6 +837,19 @@ drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
> > >>>                                     u32 output_fmt,
> > >>>                                     unsigned int *num_input_fmts);
> > >>>
> > >>> +enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
> > >>> +int drm_bridge_get_modes(struct drm_bridge *bridge,
> > >>> +                    struct drm_connector *connector);
> > >>> +struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
> > >>> +                            struct drm_connector *connector);
> > >>> +void drm_bridge_hpd_enable(struct drm_bridge *bridge,
> > >>> +                      void (*cb)(void *data,
> > >>> +                                 enum drm_connector_status status),
> > >>> +                      void *data);
> > >>> +void drm_bridge_hpd_disable(struct drm_bridge *bridge);
> > >>> +void drm_bridge_hpd_notify(struct drm_bridge *bridge,
> > >>> +                      enum drm_connector_status status);
> > >>> +
> > >>>  #ifdef CONFIG_DRM_PANEL_BRIDGE
> > >>>  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
> > >>>  struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,
> 
> -- 
> Regards,
> 
> Laurent Pinchart
Sam Ravnborg Feb. 21, 2020, 5:18 p.m. UTC | #6
Hi Laurent.

> Why ô why did I have to start the DRM/KMS documentation effort years
> ago, to see it biting me back now ? :-)
Thats obviously because you and countless others are some were nice
people that like the nice cousy feeling when you know you are doing
something to help others.
It is no your fault that some of these others are a little clueless
despite the documentation effort.
When I sometimes wander around in the kernel and then try to read the
documentation of other subsystems and fails to find it or the quality
is not just there. Then I really appreciate all the hard
effort done in the DRM subsystem.
So thumbs up, please keep up the good work all of you.

	Sam
Laurent Pinchart Feb. 22, 2020, 9:02 a.m. UTC | #7
Hi Sam,

On Fri, Feb 21, 2020 at 06:18:30PM +0100, Sam Ravnborg wrote:
> Hi Laurent.
> 
> > Why ô why did I have to start the DRM/KMS documentation effort years
> > ago, to see it biting me back now ? :-)
>
> Thats obviously because you and countless others are some were nice
> people that like the nice cousy feeling when you know you are doing
> something to help others.
> It is no your fault that some of these others are a little clueless
> despite the documentation effort.
> When I sometimes wander around in the kernel and then try to read the
> documentation of other subsystems and fails to find it or the quality
> is not just there. Then I really appreciate all the hard
> effort done in the DRM subsystem.
> So thumbs up, please keep up the good work all of you.

Thank you for the compliment. I'll do my best :-)

Patch
diff mbox series

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 68ab933ee430..78d26a9a3ee6 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -71,6 +71,8 @@  static LIST_HEAD(bridge_list);
  */
 void drm_bridge_add(struct drm_bridge *bridge)
 {
+	mutex_init(&bridge->hpd_mutex);
+
 	mutex_lock(&bridge_lock);
 	list_add_tail(&bridge->list, &bridge_list);
 	mutex_unlock(&bridge_lock);
@@ -87,6 +89,8 @@  void drm_bridge_remove(struct drm_bridge *bridge)
 	mutex_lock(&bridge_lock);
 	list_del_init(&bridge->list);
 	mutex_unlock(&bridge_lock);
+
+	mutex_destroy(&bridge->hpd_mutex);
 }
 EXPORT_SYMBOL(drm_bridge_remove);
 
@@ -919,6 +923,164 @@  int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
 }
 EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
 
+/**
+ * drm_bridge_detect - check if anything is attached to the bridge output
+ * @bridge: bridge control structure
+ *
+ * If the bridge supports output detection, as reported by the
+ * DRM_BRIDGE_OP_DETECT bridge ops flag, call &drm_bridge_funcs.detect for the
+ * bridge and return the connection status. Otherwise return
+ * connector_status_unknown.
+ *
+ * RETURNS:
+ * The detection status on success, or connector_status_unknown if the bridge
+ * doesn't support output detection.
+ */
+enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge)
+{
+	if (!(bridge->ops & DRM_BRIDGE_OP_DETECT))
+		return connector_status_unknown;
+
+	return bridge->funcs->detect(bridge);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_detect);
+
+/**
+ * drm_bridge_get_modes - fill all modes currently valid for the sink into the
+ * @connector
+ * @bridge: bridge control structure
+ * @connector: the connector to fill with modes
+ *
+ * If the bridge supports output modes retrieval, as reported by the
+ * DRM_BRIDGE_OP_MODES bridge ops flag, call &drm_bridge_funcs.get_modes to
+ * fill the connector with all valid modes and return the number of modes
+ * added. Otherwise return 0.
+ *
+ * RETURNS:
+ * The number of modes added to the connector.
+ */
+int drm_bridge_get_modes(struct drm_bridge *bridge,
+			 struct drm_connector *connector)
+{
+	if (!(bridge->ops & DRM_BRIDGE_OP_MODES))
+		return 0;
+
+	return bridge->funcs->get_modes(bridge, connector);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_get_modes);
+
+/**
+ * drm_bridge_get_edid - get the EDID data of the connected display
+ * @bridge: bridge control structure
+ * @connector: the connector to read EDID for
+ *
+ * If the bridge supports output EDID retrieval, as reported by the
+ * DRM_BRIDGE_OP_EDID bridge ops flag, call &drm_bridge_funcs.get_edid to
+ * get the EDID and return it. Otherwise return ERR_PTR(-ENOTSUPP).
+ *
+ * RETURNS:
+ * The retrieved EDID on success, or an error pointer otherwise.
+ */
+struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
+				 struct drm_connector *connector)
+{
+	if (!(bridge->ops & DRM_BRIDGE_OP_EDID))
+		return ERR_PTR(-ENOTSUPP);
+
+	return bridge->funcs->get_edid(bridge, connector);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_get_edid);
+
+/**
+ * drm_bridge_hpd_enable - enable hot plug detection for the bridge
+ * @bridge: bridge control structure
+ * @cb: hot-plug detection callback
+ * @data: data to be passed to the hot-plug detection callback
+ *
+ * Call &drm_bridge_funcs.hpd_enable if implemented and register the given @cb
+ * and @data as hot plug notification callback. From now on the @cb will be
+ * called with @data when an output status change is detected by the bridge,
+ * until hot plug notification gets disabled with drm_bridge_hpd_disable().
+ *
+ * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
+ * bridge->ops. This function shall not be called when the flag is not set.
+ *
+ * Only one hot plug detection callback can be registered at a time, it is an
+ * error to call this function when hot plug detection is already enabled for
+ * the bridge.
+ */
+void drm_bridge_hpd_enable(struct drm_bridge *bridge,
+			   void (*cb)(void *data,
+				      enum drm_connector_status status),
+			   void *data)
+{
+	if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
+		return;
+
+	mutex_lock(&bridge->hpd_mutex);
+
+	if (WARN(bridge->hpd_cb, "Hot plug detection already enabled\n"))
+		goto unlock;
+
+	bridge->hpd_cb = cb;
+	bridge->hpd_data = data;
+
+	if (bridge->funcs->hpd_enable)
+		bridge->funcs->hpd_enable(bridge);
+
+unlock:
+	mutex_unlock(&bridge->hpd_mutex);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_hpd_enable);
+
+/**
+ * drm_bridge_hpd_disable - disable hot plug detection for the bridge
+ * @bridge: bridge control structure
+ *
+ * Call &drm_bridge_funcs.hpd_disable if implemented and unregister the hot
+ * plug detection callback previously registered with drm_bridge_hpd_enable().
+ * Once this function returns the callback will not be called by the bridge
+ * when an output status change occurs.
+ *
+ * Hot plug detection is supported only if the DRM_BRIDGE_OP_HPD flag is set in
+ * bridge->ops. This function shall not be called when the flag is not set.
+ */
+void drm_bridge_hpd_disable(struct drm_bridge *bridge)
+{
+	if (!bridge || !(bridge->ops & DRM_BRIDGE_OP_HPD))
+		return;
+
+	mutex_lock(&bridge->hpd_mutex);
+	if (bridge->funcs->hpd_disable)
+		bridge->funcs->hpd_disable(bridge);
+
+	bridge->hpd_cb = NULL;
+	bridge->hpd_data = NULL;
+	mutex_unlock(&bridge->hpd_mutex);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_hpd_disable);
+
+/**
+ * drm_bridge_hpd_notify - notify hot plug detection events
+ * @bridge: bridge control structure
+ * @status: output connection status
+ *
+ * Bridge drivers shall call this function to report hot plug events when they
+ * detect a change in the output status, when hot plug detection has been
+ * enabled by drm_bridge_hpd_enable().
+ *
+ * This function shall be called in a context that can sleep.
+ */
+void drm_bridge_hpd_notify(struct drm_bridge *bridge,
+			   enum drm_connector_status status)
+{
+	mutex_lock(&bridge->hpd_mutex);
+	if (bridge->hpd_cb)
+		bridge->hpd_cb(bridge->hpd_data, status);
+	mutex_unlock(&bridge->hpd_mutex);
+}
+EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
+
 #ifdef CONFIG_OF
 /**
  * of_drm_find_bridge - find the bridge corresponding to the device node in
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 45626ecf20f8..ba9b7c84f11e 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -23,8 +23,9 @@ 
 #ifndef __DRM_BRIDGE_H__
 #define __DRM_BRIDGE_H__
 
-#include <linux/list.h>
 #include <linux/ctype.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_encoder.h>
@@ -33,7 +34,10 @@ 
 
 struct drm_bridge;
 struct drm_bridge_timings;
+struct drm_connector;
 struct drm_panel;
+struct edid;
+struct i2c_adapter;
 
 /**
  * struct drm_bridge_funcs - drm_bridge control functions
@@ -488,6 +492,119 @@  struct drm_bridge_funcs {
 	 * giving the reason of the failure otherwise.
 	 */
 	struct drm_bridge_state *(*atomic_reset)(struct drm_bridge *bridge);
+
+	/**
+	 * @detect:
+	 *
+	 * Check if anything is attached to the bridge output.
+	 *
+	 * This callback is optional, if not implemented the bridge will be
+	 * considered as always having a component attached to its output.
+	 * Bridges that implement this callback shall set the
+	 * DRM_BRIDGE_OP_DETECT flag in their &drm_bridge->ops.
+	 *
+	 * RETURNS:
+	 *
+	 * drm_connector_status indicating the bridge output status.
+	 */
+	enum drm_connector_status (*detect)(struct drm_bridge *bridge);
+
+	/**
+	 * @get_modes:
+	 *
+	 * Fill all modes currently valid for the sink into the &drm_connector
+	 * with drm_mode_probed_add().
+	 *
+	 * The @get_modes callback is mostly intended to support non-probeable
+	 * displays such as many fixed panels. Bridges that support reading
+	 * EDID shall leave @get_modes unimplemented and implement the
+	 * &drm_bridge_funcs->get_edid callback instead.
+	 *
+	 * This callback is optional. Bridges that implement it shall set the
+	 * DRM_BRIDGE_OP_MODES flag in their &drm_bridge->ops.
+	 *
+	 * The connector parameter shall be used for the sole purpose of
+	 * filling modes, and shall not be stored internally by bridge drivers
+	 * for future usage.
+	 *
+	 * RETURNS:
+	 *
+	 * The number of modes added by calling drm_mode_probed_add().
+	 */
+	int (*get_modes)(struct drm_bridge *bridge,
+			 struct drm_connector *connector);
+
+	/**
+	 * @get_edid:
+	 *
+	 * Read and parse the EDID data of the connected display.
+	 *
+	 * The @get_edid callback is the preferred way of reporting mode
+	 * information for a display connected to the bridge output. Bridges
+	 * that support reading EDID shall implement this callback and leave
+	 * the @get_modes callback unimplemented.
+	 *
+	 * The caller of this operation shall first verify the output
+	 * connection status and refrain from reading EDID from a disconnected
+	 * output.
+	 *
+	 * This callback is optional. Bridges that implement it shall set the
+	 * DRM_BRIDGE_OP_EDID flag in their &drm_bridge->ops.
+	 *
+	 * The connector parameter shall be used for the sole purpose of EDID
+	 * retrieval and parsing, and shall not be stored internally by bridge
+	 * drivers for future usage.
+	 *
+	 * RETURNS:
+	 *
+	 * An edid structure newly allocated with kmalloc() (or similar) on
+	 * success, or NULL otherwise. The caller is responsible for freeing
+	 * the returned edid structure with kfree().
+	 */
+	struct edid *(*get_edid)(struct drm_bridge *bridge,
+				 struct drm_connector *connector);
+
+	/**
+	 * @hpd_notify:
+	 *
+	 * Notify the bridge of hot plug detection.
+	 *
+	 * This callback is optional, it may be implemented by bridges that
+	 * need to be notified of display connection or disconnection for
+	 * internal reasons. One use case is to reset the internal state of CEC
+	 * controllers for HDMI bridges.
+	 */
+	void (*hpd_notify)(struct drm_bridge *bridge,
+			   enum drm_connector_status status);
+
+	/**
+	 * @hpd_enable:
+	 *
+	 * Enable hot plug detection. From now on the bridge shall call
+	 * drm_bridge_hpd_notify() each time a change is detected in the output
+	 * connection status, until hot plug detection gets disabled with
+	 * @hpd_disable.
+	 *
+	 * This callback is optional and shall only be implemented by bridges
+	 * that support hot-plug notification without polling. Bridges that
+	 * implement it shall also implement the @hpd_disable callback and set
+	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
+	 */
+	void (*hpd_enable)(struct drm_bridge *bridge);
+
+	/**
+	 * @hpd_disable:
+	 *
+	 * Disable hot plug detection. Once this function returns the bridge
+	 * shall not call drm_bridge_hpd_notify() when a change in the output
+	 * connection status occurs.
+	 *
+	 * This callback is optional and shall only be implemented by bridges
+	 * that support hot-plug notification without polling. Bridges that
+	 * implement it shall also implement the @hpd_enable callback and set
+	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
+	 */
+	void (*hpd_disable)(struct drm_bridge *bridge);
 };
 
 /**
@@ -526,6 +643,39 @@  struct drm_bridge_timings {
 	bool dual_link;
 };
 
+/**
+ * enum drm_bridge_ops - Bitmask of operations supported by the bridge
+ */
+enum drm_bridge_ops {
+	/**
+	 * @DRM_BRIDGE_OP_DETECT: The bridge can detect displays connected to
+	 * its output. Bridges that set this flag shall implement the
+	 * &drm_bridge_funcs->detect callback.
+	 */
+	DRM_BRIDGE_OP_DETECT = BIT(0),
+	/**
+	 * @DRM_BRIDGE_OP_EDID: The bridge can retrieve the EDID of the display
+	 * connected to its output. Bridges that set this flag shall implement
+	 * the &drm_bridge_funcs->get_edid callback.
+	 */
+	DRM_BRIDGE_OP_EDID = BIT(1),
+	/**
+	 * @DRM_BRIDGE_OP_HPD: The bridge can detect hot-plug and hot-unplug
+	 * without requiring polling. Bridges that set this flag shall
+	 * implement the &drm_bridge_funcs->hpd_enable and
+	 * &drm_bridge_funcs->hpd_disable callbacks if they support enabling
+	 * and disabling hot-plug detection dynamically.
+	 */
+	DRM_BRIDGE_OP_HPD = BIT(2),
+	/**
+	 * @DRM_BRIDGE_OP_MODES: The bridge can retrieve the modes supported
+	 * by the display at its output. This does not include reading EDID
+	 * which is separately covered by @DRM_BRIDGE_OP_EDID. Bridges that set
+	 * this flag shall implement the &drm_bridge_funcs->get_modes callback.
+	 */
+	DRM_BRIDGE_OP_MODES = BIT(3),
+};
+
 /**
  * struct drm_bridge - central DRM bridge control structure
  */
@@ -554,6 +704,33 @@  struct drm_bridge {
 	const struct drm_bridge_funcs *funcs;
 	/** @driver_private: pointer to the bridge driver's internal context */
 	void *driver_private;
+	/** @ops: bitmask of operations supported by the bridge */
+	enum drm_bridge_ops ops;
+	/**
+	 * @type: Type of the connection at the bridge output
+	 * (DRM_MODE_CONNECTOR_*). For bridges at the end of this chain this
+	 * identifies the type of connected display.
+	 */
+	int type;
+	/**
+	 * @ddc: Associated I2C adapter for DDC access, if any.
+	 */
+	struct i2c_adapter *ddc;
+	/** private: */
+	/**
+	 * @hpd_mutex: Protects the @hpd_cb and @hpd_data fields.
+	 */
+	struct mutex hpd_mutex;
+	/**
+	 * @hpd_cb: Hot plug detection callback, registered with
+	 * drm_bridge_hpd_enable().
+	 */
+	void (*hpd_cb)(void *data, enum drm_connector_status status);
+	/**
+	 * @hpd_data: Private data passed to the Hot plug detection callback
+	 * @hpd_cb.
+	 */
+	void *hpd_data;
 };
 
 static inline struct drm_bridge *
@@ -660,6 +837,19 @@  drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
 					u32 output_fmt,
 					unsigned int *num_input_fmts);
 
+enum drm_connector_status drm_bridge_detect(struct drm_bridge *bridge);
+int drm_bridge_get_modes(struct drm_bridge *bridge,
+			 struct drm_connector *connector);
+struct edid *drm_bridge_get_edid(struct drm_bridge *bridge,
+				 struct drm_connector *connector);
+void drm_bridge_hpd_enable(struct drm_bridge *bridge,
+			   void (*cb)(void *data,
+				      enum drm_connector_status status),
+			   void *data);
+void drm_bridge_hpd_disable(struct drm_bridge *bridge);
+void drm_bridge_hpd_notify(struct drm_bridge *bridge,
+			   enum drm_connector_status status);
+
 #ifdef CONFIG_DRM_PANEL_BRIDGE
 struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
 struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,