[v3,03/22] drm: Add get_vblank_timestamp() to struct drm_crtc_funcs
diff mbox series

Message ID 20200120082314.14756-4-tzimmermann@suse.de
State Superseded
Headers show
Series
  • drm: Clean up VBLANK callbacks in struct drm_driver
Related show

Commit Message

Thomas Zimmermann Jan. 20, 2020, 8:22 a.m. UTC
The callback get_vblank_timestamp() is currently located in struct
drm_driver, but really belongs into struct drm_crtc_funcs. Add an
equivalent there. Driver will be converted in separate patches.

The default implementation is drm_calc_vbltimestamp_from_scanoutpos().
The patch adds drm_crtc_vblank_helper_get_vblank_timestamp(), which is
an implementation for the CRTC callback.

v3:
	* use refactored timestamp calculation to minimize duplicated code
	* do more checks for crtc != NULL to support legacy drivers
v2:
	* rename helper to drm_crtc_vblank_helper_get_vblank_timestamp()
	* replace drm_calc_vbltimestamp_from_scanoutpos() with
	  drm_crtc_vblank_helper_get_vblank_timestamp() in docs

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/drm_vblank.c             | 74 +++++++++++++++++++++---
 include/drm/drm_crtc.h                   | 46 ++++++++++++++-
 include/drm/drm_modeset_helper_vtables.h |  4 +-
 include/drm/drm_vblank.h                 | 16 +++--
 4 files changed, 123 insertions(+), 17 deletions(-)

Comments

Ville Syrjälä Jan. 20, 2020, 3:38 p.m. UTC | #1
On Mon, Jan 20, 2020 at 09:22:55AM +0100, Thomas Zimmermann wrote:
> The callback get_vblank_timestamp() is currently located in struct
> drm_driver, but really belongs into struct drm_crtc_funcs. Add an
> equivalent there. Driver will be converted in separate patches.
> 
> The default implementation is drm_calc_vbltimestamp_from_scanoutpos().
> The patch adds drm_crtc_vblank_helper_get_vblank_timestamp(), which is
> an implementation for the CRTC callback.
> 
> v3:
> 	* use refactored timestamp calculation to minimize duplicated code
> 	* do more checks for crtc != NULL to support legacy drivers
> v2:
> 	* rename helper to drm_crtc_vblank_helper_get_vblank_timestamp()
> 	* replace drm_calc_vbltimestamp_from_scanoutpos() with
> 	  drm_crtc_vblank_helper_get_vblank_timestamp() in docs
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/drm_vblank.c             | 74 +++++++++++++++++++++---
>  include/drm/drm_crtc.h                   | 46 ++++++++++++++-
>  include/drm/drm_modeset_helper_vtables.h |  4 +-
>  include/drm/drm_vblank.h                 | 16 +++--
>  4 files changed, 123 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 7e962c29780c..fc297043e3ba 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -333,7 +333,9 @@ u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)
>  	u64 vblank;
>  	unsigned long flags;
>  
> -	WARN_ONCE(drm_debug_enabled(DRM_UT_VBL) && !dev->driver->get_vblank_timestamp,
> +	WARN_ONCE(drm_debug_enabled(DRM_UT_VBL) &&
> +		  !crtc->funcs->get_vblank_timestamp &&
> +		  !dev->driver->get_vblank_timestamp,
>  		  "This function requires support for accurate vblank timestamps.");
>  
>  	spin_lock_irqsave(&dev->vblank_time_lock, flags);
> @@ -511,9 +513,9 @@ EXPORT_SYMBOL(drm_crtc_vblank_waitqueue);
>   *
>   * Calculate and store various constants which are later needed by vblank and
>   * swap-completion timestamping, e.g, by
> - * drm_calc_vbltimestamp_from_scanoutpos(). They are derived from CRTC's true
> - * scanout timing, so they take things like panel scaling or other adjustments
> - * into account.
> + * drm_crtc_vblank_helper_get_vblank_timestamp(). They are derived from
> + * CRTC's true scanout timing, so they take things like panel scaling or
> + * other adjustments into account.
>   */
>  void drm_calc_timestamping_constants(struct drm_crtc *crtc,
>  				     const struct drm_display_mode *mode)
> @@ -577,8 +579,9 @@ EXPORT_SYMBOL(drm_calc_timestamping_constants);
>   *
>   * Implements calculation of exact vblank timestamps from given drm_display_mode
>   * timings and current video scanout position of a CRTC. This can be directly
> - * used as the &drm_driver.get_vblank_timestamp implementation of a kms driver
> - * if &drm_crtc_helper_funcs.get_scanout_position is implemented.
> + * used as the &drm_crtc_funcs.get_vblank_timestamp implementation of a kms
> + * driver if &drm_crtc_helper_funcs.get_scanout_position or
> + * &drm_driver.get_scanout_position is implemented.
>   *
>   * The current implementation only handles standard video modes. For double scan
>   * and interlaced modes the driver is supposed to adjust the hardware mode
> @@ -774,6 +777,48 @@ drm_crtc_vblank_helper_get_vblank_timestamp_internal(
>  }
>  EXPORT_SYMBOL(drm_crtc_vblank_helper_get_vblank_timestamp_internal);
>  
> +/**
> + * drm_crtc_vblank_helper_get_vblank_timestamp - precise vblank timestamp
> + *                                               helper
> + * @crtc: CRTC whose vblank timestamp to retrieve
> + * @max_error: Desired maximum allowable error in timestamps (nanosecs)
> + *             On return contains true maximum error of timestamp
> + * @vblank_time: Pointer to time which should receive the timestamp
> + * @in_vblank_irq:
> + *     True when called from drm_crtc_handle_vblank().  Some drivers
> + *     need to apply some workarounds for gpu-specific vblank irq quirks
> + *     if flag is set.
> + *
> + * Implements calculation of exact vblank timestamps from given drm_display_mode
> + * timings and current video scanout position of a CRTC. This can be directly
> + * used as the &drm_crtc_funcs.get_vblank_timestamp implementation of a kms
> + * driver if &drm_crtc_helper_funcs.get_scanout_position is implemented.
> + *
> + * The current implementation only handles standard video modes. For double scan
> + * and interlaced modes the driver is supposed to adjust the hardware mode
> + * (taken from &drm_crtc_state.adjusted mode for atomic modeset drivers) to
> + * match the scanout position reported.
> + *
> + * Note that atomic drivers must call drm_calc_timestamping_constants() before
> + * enabling a CRTC. The atomic helpers already take care of that in
> + * drm_atomic_helper_update_legacy_modeset_state().
> + *
> + * Returns:
> + *
> + * Returns true on success, and false on failure, i.e. when no accurate
> + * timestamp could be acquired.
> + */
> +bool drm_crtc_vblank_helper_get_vblank_timestamp(struct drm_crtc *crtc,
> +						 int *max_error,
> +						 ktime_t *vblank_time,
> +						 bool in_vblank_irq)
> +{
> +	return drm_crtc_vblank_helper_get_vblank_timestamp_internal(
> +		crtc, max_error, vblank_time, in_vblank_irq,
> +		crtc->helper_private->get_scanout_position, NULL);
> +}
> +EXPORT_SYMBOL(drm_crtc_vblank_helper_get_vblank_timestamp);
> +
>  /**
>   * drm_get_last_vbltimestamp - retrieve raw timestamp for the most recent
>   *                             vblank interval
> @@ -799,15 +844,22 @@ static bool
>  drm_get_last_vbltimestamp(struct drm_device *dev, unsigned int pipe,
>  			  ktime_t *tvblank, bool in_vblank_irq)
>  {
> +	struct drm_crtc *crtc = drm_crtc_from_index(dev, pipe);
>  	bool ret = false;
>  
>  	/* Define requested maximum error on timestamps (nanoseconds). */
>  	int max_error = (int) drm_timestamp_precision * 1000;
>  
>  	/* Query driver if possible and precision timestamping enabled. */
> -	if (dev->driver->get_vblank_timestamp && (max_error > 0))
> +	if (crtc && crtc->funcs->get_vblank_timestamp && max_error > 0) {
> +		struct drm_crtc *crtc = drm_crtc_from_index(dev, pipe);
> +
> +		ret = crtc->funcs->get_vblank_timestamp(crtc, &max_error,
> +							tvblank, in_vblank_irq);
> +	} else if (dev->driver->get_vblank_timestamp && max_error > 0) {
>  		ret = dev->driver->get_vblank_timestamp(dev, pipe, &max_error,
>  							tvblank, in_vblank_irq);
> +	}
>  
>  	/* GPU high precision timestamp query unsupported or failed.
>  	 * Return current monotonic/gettimeofday timestamp as best estimate.
> @@ -1790,9 +1842,11 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
>  
>  static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
>  {
> +	struct drm_crtc *crtc = drm_crtc_from_index(dev, pipe);
>  	struct drm_pending_vblank_event *e, *t;
>  	ktime_t now;
>  	u64 seq;
> +	bool high_prec;
>  
>  	assert_spin_locked(&dev->event_lock);
>  
> @@ -1812,8 +1866,10 @@ static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
>  		send_vblank_event(dev, e, seq, now);
>  	}
>  
> -	trace_drm_vblank_event(pipe, seq, now,
> -			dev->driver->get_vblank_timestamp != NULL);
> +	high_prec = crtc && crtc->funcs->get_vblank_timestamp ||
> +		    dev->driver->get_vblank_timestamp;

I'm sure gcc will complain about the && vs. || here. Hmm, yeah looks
like quite a few gcc/sparse/checkpatch warnings in this series.

With some of the more important warns fixed patches 1-3 are
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> +
> +	trace_drm_vblank_event(pipe, seq, now, high_prec);
>  }
>  
>  /**
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 5e9b15a0e8c5..db46abbbf4e7 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -867,6 +867,47 @@ struct drm_crtc_funcs {
>  	 * new drivers as the replacement of &drm_driver.disable_vblank hook.
>  	 */
>  	void (*disable_vblank)(struct drm_crtc *crtc);
> +
> +	/**
> +	 * @get_vblank_timestamp:
> +	 *
> +	 * Called by drm_get_last_vbltimestamp(). Should return a precise
> +	 * timestamp when the most recent vblank interval ended or will end.
> +	 *
> +	 * Specifically, the timestamp in @vblank_time should correspond as
> +	 * closely as possible to the time when the first video scanline of
> +	 * the video frame after the end of vblank will start scanning out,
> +	 * the time immediately after end of the vblank interval. If the
> +	 * @crtc is currently inside vblank, this will be a time in the future.
> +	 * If the @crtc is currently scanning out a frame, this will be the
> +	 * past start time of the current scanout. This is meant to adhere
> +	 * to the OpenML OML_sync_control extension specification.
> +	 *
> +	 * Parameters:
> +	 *
> +	 * crtc:
> +	 *     CRTC for which timestamp should be returned.
> +	 * max_error:
> +	 *     Maximum allowable timestamp error in nanoseconds.
> +	 *     Implementation should strive to provide timestamp
> +	 *     with an error of at most max_error nanoseconds.
> +	 *     Returns true upper bound on error for timestamp.
> +	 * vblank_time:
> +	 *     Target location for returned vblank timestamp.
> +	 * in_vblank_irq:
> +	 *     True when called from drm_crtc_handle_vblank().  Some drivers
> +	 *     need to apply some workarounds for gpu-specific vblank irq quirks
> +	 *     if flag is set.
> +	 *
> +	 * Returns:
> +	 *
> +	 * True on success, false on failure, which means the core should
> +	 * fallback to a simple timestamp taken in drm_crtc_handle_vblank().
> +	 */
> +	bool (*get_vblank_timestamp)(struct drm_crtc *crtc,
> +				     int *max_error,
> +				     ktime_t *vblank_time,
> +				     bool in_vblank_irq);
>  };
>  
>  /**
> @@ -974,11 +1015,12 @@ struct drm_crtc {
>  	 * Programmed mode in hw, after adjustments for encoders, crtc, panel
>  	 * scaling etc. Should only be used by legacy drivers, for high
>  	 * precision vblank timestamps in
> -	 * drm_calc_vbltimestamp_from_scanoutpos().
> +	 * drm_crtc_vblank_helper_get_vblank_timestamp().
>  	 *
>  	 * Note that atomic drivers should not use this, but instead use
>  	 * &drm_crtc_state.adjusted_mode. And for high-precision timestamps
> -	 * drm_calc_vbltimestamp_from_scanoutpos() used &drm_vblank_crtc.hwmode,
> +	 * drm_crtc_vblank_helper_get_vblank_timestamp() used
> +	 * &drm_vblank_crtc.hwmode,
>  	 * which is filled out by calling drm_calc_timestamping_constants().
>  	 */
>  	struct drm_display_mode hwmode;
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index e398512bfd5f..0afaf58da40d 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -459,8 +459,8 @@ struct drm_crtc_helper_funcs {
>  	 * Returns the current display scanout position from a CRTC and an
>  	 * optional accurate ktime_get() timestamp of when the position was
>  	 * measured. Note that this is a helper callback which is only used
> -	 * if a driver uses drm_calc_vbltimestamp_from_scanoutpos() for the
> -	 * @drm_driver.get_vblank_timestamp callback.
> +	 * if a driver uses drm_crtc_vblank_helper_get_vblank_timestamp()
> +	 * for the @drm_crtc_funcs.get_vblank_timestamp callback.
>  	 *
>  	 * Parameters:
>  	 *
> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> index 1c84e99b3f4f..4bfffe990828 100644
> --- a/include/drm/drm_vblank.h
> +++ b/include/drm/drm_vblank.h
> @@ -174,13 +174,13 @@ struct drm_vblank_crtc {
>  	unsigned int pipe;
>  	/**
>  	 * @framedur_ns: Frame/Field duration in ns, used by
> -	 * drm_calc_vbltimestamp_from_scanoutpos() and computed by
> +	 * drm_crtc_vblank_helper_get_vblank_timestamp() and computed by
>  	 * drm_calc_timestamping_constants().
>  	 */
>  	int framedur_ns;
>  	/**
>  	 * @linedur_ns: Line duration in ns, used by
> -	 * drm_calc_vbltimestamp_from_scanoutpos() and computed by
> +	 * drm_crtc_vblank_helper_get_vblank_timestamp() and computed by
>  	 * drm_calc_timestamping_constants().
>  	 */
>  	int linedur_ns;
> @@ -190,8 +190,8 @@ struct drm_vblank_crtc {
>  	 *
>  	 * Cache of the current hardware display mode. Only valid when @enabled
>  	 * is set. This is used by helpers like
> -	 * drm_calc_vbltimestamp_from_scanoutpos(). We can't just access the
> -	 * hardware mode by e.g. looking at &drm_crtc_state.adjusted_mode,
> +	 * drm_crtc_vblank_helper_get_vblank_timestamp(). We can't just access
> +	 * the hardware mode by e.g. looking at &drm_crtc_state.adjusted_mode,
>  	 * because that one is really hard to get from interrupt context.
>  	 */
>  	struct drm_display_mode hwmode;
> @@ -239,6 +239,10 @@ wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
>  void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
>  				   u32 max_vblank_count);
>  
> +/*
> + * Helpers for struct drm_crtc_funcs
> + */
> +
>  typedef bool (*drm_vblank_get_scanout_position_func)(struct drm_crtc *crtc,
>  						     bool in_vblank_irq,
>  						     int *vpos, int *hpos,
> @@ -259,5 +263,9 @@ drm_crtc_vblank_helper_get_vblank_timestamp_internal(struct drm_crtc *crtc,
>  						     bool in_vblank_irq,
>  						     drm_vblank_get_scanout_position_func get_scanout_position,
>  						     drm_vblank_get_scanout_position_legacy_func get_scanout_position_legacy);
> +bool drm_crtc_vblank_helper_get_vblank_timestamp(struct drm_crtc *crtc,
> +						 int *max_error,
> +						 ktime_t *vblank_time,
> +						 bool in_vblank_irq);
>  
>  #endif
> -- 
> 2.24.1
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

Patch
diff mbox series

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 7e962c29780c..fc297043e3ba 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -333,7 +333,9 @@  u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc)
 	u64 vblank;
 	unsigned long flags;
 
-	WARN_ONCE(drm_debug_enabled(DRM_UT_VBL) && !dev->driver->get_vblank_timestamp,
+	WARN_ONCE(drm_debug_enabled(DRM_UT_VBL) &&
+		  !crtc->funcs->get_vblank_timestamp &&
+		  !dev->driver->get_vblank_timestamp,
 		  "This function requires support for accurate vblank timestamps.");
 
 	spin_lock_irqsave(&dev->vblank_time_lock, flags);
@@ -511,9 +513,9 @@  EXPORT_SYMBOL(drm_crtc_vblank_waitqueue);
  *
  * Calculate and store various constants which are later needed by vblank and
  * swap-completion timestamping, e.g, by
- * drm_calc_vbltimestamp_from_scanoutpos(). They are derived from CRTC's true
- * scanout timing, so they take things like panel scaling or other adjustments
- * into account.
+ * drm_crtc_vblank_helper_get_vblank_timestamp(). They are derived from
+ * CRTC's true scanout timing, so they take things like panel scaling or
+ * other adjustments into account.
  */
 void drm_calc_timestamping_constants(struct drm_crtc *crtc,
 				     const struct drm_display_mode *mode)
@@ -577,8 +579,9 @@  EXPORT_SYMBOL(drm_calc_timestamping_constants);
  *
  * Implements calculation of exact vblank timestamps from given drm_display_mode
  * timings and current video scanout position of a CRTC. This can be directly
- * used as the &drm_driver.get_vblank_timestamp implementation of a kms driver
- * if &drm_crtc_helper_funcs.get_scanout_position is implemented.
+ * used as the &drm_crtc_funcs.get_vblank_timestamp implementation of a kms
+ * driver if &drm_crtc_helper_funcs.get_scanout_position or
+ * &drm_driver.get_scanout_position is implemented.
  *
  * The current implementation only handles standard video modes. For double scan
  * and interlaced modes the driver is supposed to adjust the hardware mode
@@ -774,6 +777,48 @@  drm_crtc_vblank_helper_get_vblank_timestamp_internal(
 }
 EXPORT_SYMBOL(drm_crtc_vblank_helper_get_vblank_timestamp_internal);
 
+/**
+ * drm_crtc_vblank_helper_get_vblank_timestamp - precise vblank timestamp
+ *                                               helper
+ * @crtc: CRTC whose vblank timestamp to retrieve
+ * @max_error: Desired maximum allowable error in timestamps (nanosecs)
+ *             On return contains true maximum error of timestamp
+ * @vblank_time: Pointer to time which should receive the timestamp
+ * @in_vblank_irq:
+ *     True when called from drm_crtc_handle_vblank().  Some drivers
+ *     need to apply some workarounds for gpu-specific vblank irq quirks
+ *     if flag is set.
+ *
+ * Implements calculation of exact vblank timestamps from given drm_display_mode
+ * timings and current video scanout position of a CRTC. This can be directly
+ * used as the &drm_crtc_funcs.get_vblank_timestamp implementation of a kms
+ * driver if &drm_crtc_helper_funcs.get_scanout_position is implemented.
+ *
+ * The current implementation only handles standard video modes. For double scan
+ * and interlaced modes the driver is supposed to adjust the hardware mode
+ * (taken from &drm_crtc_state.adjusted mode for atomic modeset drivers) to
+ * match the scanout position reported.
+ *
+ * Note that atomic drivers must call drm_calc_timestamping_constants() before
+ * enabling a CRTC. The atomic helpers already take care of that in
+ * drm_atomic_helper_update_legacy_modeset_state().
+ *
+ * Returns:
+ *
+ * Returns true on success, and false on failure, i.e. when no accurate
+ * timestamp could be acquired.
+ */
+bool drm_crtc_vblank_helper_get_vblank_timestamp(struct drm_crtc *crtc,
+						 int *max_error,
+						 ktime_t *vblank_time,
+						 bool in_vblank_irq)
+{
+	return drm_crtc_vblank_helper_get_vblank_timestamp_internal(
+		crtc, max_error, vblank_time, in_vblank_irq,
+		crtc->helper_private->get_scanout_position, NULL);
+}
+EXPORT_SYMBOL(drm_crtc_vblank_helper_get_vblank_timestamp);
+
 /**
  * drm_get_last_vbltimestamp - retrieve raw timestamp for the most recent
  *                             vblank interval
@@ -799,15 +844,22 @@  static bool
 drm_get_last_vbltimestamp(struct drm_device *dev, unsigned int pipe,
 			  ktime_t *tvblank, bool in_vblank_irq)
 {
+	struct drm_crtc *crtc = drm_crtc_from_index(dev, pipe);
 	bool ret = false;
 
 	/* Define requested maximum error on timestamps (nanoseconds). */
 	int max_error = (int) drm_timestamp_precision * 1000;
 
 	/* Query driver if possible and precision timestamping enabled. */
-	if (dev->driver->get_vblank_timestamp && (max_error > 0))
+	if (crtc && crtc->funcs->get_vblank_timestamp && max_error > 0) {
+		struct drm_crtc *crtc = drm_crtc_from_index(dev, pipe);
+
+		ret = crtc->funcs->get_vblank_timestamp(crtc, &max_error,
+							tvblank, in_vblank_irq);
+	} else if (dev->driver->get_vblank_timestamp && max_error > 0) {
 		ret = dev->driver->get_vblank_timestamp(dev, pipe, &max_error,
 							tvblank, in_vblank_irq);
+	}
 
 	/* GPU high precision timestamp query unsupported or failed.
 	 * Return current monotonic/gettimeofday timestamp as best estimate.
@@ -1790,9 +1842,11 @@  int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
 
 static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
 {
+	struct drm_crtc *crtc = drm_crtc_from_index(dev, pipe);
 	struct drm_pending_vblank_event *e, *t;
 	ktime_t now;
 	u64 seq;
+	bool high_prec;
 
 	assert_spin_locked(&dev->event_lock);
 
@@ -1812,8 +1866,10 @@  static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
 		send_vblank_event(dev, e, seq, now);
 	}
 
-	trace_drm_vblank_event(pipe, seq, now,
-			dev->driver->get_vblank_timestamp != NULL);
+	high_prec = crtc && crtc->funcs->get_vblank_timestamp ||
+		    dev->driver->get_vblank_timestamp;
+
+	trace_drm_vblank_event(pipe, seq, now, high_prec);
 }
 
 /**
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 5e9b15a0e8c5..db46abbbf4e7 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -867,6 +867,47 @@  struct drm_crtc_funcs {
 	 * new drivers as the replacement of &drm_driver.disable_vblank hook.
 	 */
 	void (*disable_vblank)(struct drm_crtc *crtc);
+
+	/**
+	 * @get_vblank_timestamp:
+	 *
+	 * Called by drm_get_last_vbltimestamp(). Should return a precise
+	 * timestamp when the most recent vblank interval ended or will end.
+	 *
+	 * Specifically, the timestamp in @vblank_time should correspond as
+	 * closely as possible to the time when the first video scanline of
+	 * the video frame after the end of vblank will start scanning out,
+	 * the time immediately after end of the vblank interval. If the
+	 * @crtc is currently inside vblank, this will be a time in the future.
+	 * If the @crtc is currently scanning out a frame, this will be the
+	 * past start time of the current scanout. This is meant to adhere
+	 * to the OpenML OML_sync_control extension specification.
+	 *
+	 * Parameters:
+	 *
+	 * crtc:
+	 *     CRTC for which timestamp should be returned.
+	 * max_error:
+	 *     Maximum allowable timestamp error in nanoseconds.
+	 *     Implementation should strive to provide timestamp
+	 *     with an error of at most max_error nanoseconds.
+	 *     Returns true upper bound on error for timestamp.
+	 * vblank_time:
+	 *     Target location for returned vblank timestamp.
+	 * in_vblank_irq:
+	 *     True when called from drm_crtc_handle_vblank().  Some drivers
+	 *     need to apply some workarounds for gpu-specific vblank irq quirks
+	 *     if flag is set.
+	 *
+	 * Returns:
+	 *
+	 * True on success, false on failure, which means the core should
+	 * fallback to a simple timestamp taken in drm_crtc_handle_vblank().
+	 */
+	bool (*get_vblank_timestamp)(struct drm_crtc *crtc,
+				     int *max_error,
+				     ktime_t *vblank_time,
+				     bool in_vblank_irq);
 };
 
 /**
@@ -974,11 +1015,12 @@  struct drm_crtc {
 	 * Programmed mode in hw, after adjustments for encoders, crtc, panel
 	 * scaling etc. Should only be used by legacy drivers, for high
 	 * precision vblank timestamps in
-	 * drm_calc_vbltimestamp_from_scanoutpos().
+	 * drm_crtc_vblank_helper_get_vblank_timestamp().
 	 *
 	 * Note that atomic drivers should not use this, but instead use
 	 * &drm_crtc_state.adjusted_mode. And for high-precision timestamps
-	 * drm_calc_vbltimestamp_from_scanoutpos() used &drm_vblank_crtc.hwmode,
+	 * drm_crtc_vblank_helper_get_vblank_timestamp() used
+	 * &drm_vblank_crtc.hwmode,
 	 * which is filled out by calling drm_calc_timestamping_constants().
 	 */
 	struct drm_display_mode hwmode;
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index e398512bfd5f..0afaf58da40d 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -459,8 +459,8 @@  struct drm_crtc_helper_funcs {
 	 * Returns the current display scanout position from a CRTC and an
 	 * optional accurate ktime_get() timestamp of when the position was
 	 * measured. Note that this is a helper callback which is only used
-	 * if a driver uses drm_calc_vbltimestamp_from_scanoutpos() for the
-	 * @drm_driver.get_vblank_timestamp callback.
+	 * if a driver uses drm_crtc_vblank_helper_get_vblank_timestamp()
+	 * for the @drm_crtc_funcs.get_vblank_timestamp callback.
 	 *
 	 * Parameters:
 	 *
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 1c84e99b3f4f..4bfffe990828 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -174,13 +174,13 @@  struct drm_vblank_crtc {
 	unsigned int pipe;
 	/**
 	 * @framedur_ns: Frame/Field duration in ns, used by
-	 * drm_calc_vbltimestamp_from_scanoutpos() and computed by
+	 * drm_crtc_vblank_helper_get_vblank_timestamp() and computed by
 	 * drm_calc_timestamping_constants().
 	 */
 	int framedur_ns;
 	/**
 	 * @linedur_ns: Line duration in ns, used by
-	 * drm_calc_vbltimestamp_from_scanoutpos() and computed by
+	 * drm_crtc_vblank_helper_get_vblank_timestamp() and computed by
 	 * drm_calc_timestamping_constants().
 	 */
 	int linedur_ns;
@@ -190,8 +190,8 @@  struct drm_vblank_crtc {
 	 *
 	 * Cache of the current hardware display mode. Only valid when @enabled
 	 * is set. This is used by helpers like
-	 * drm_calc_vbltimestamp_from_scanoutpos(). We can't just access the
-	 * hardware mode by e.g. looking at &drm_crtc_state.adjusted_mode,
+	 * drm_crtc_vblank_helper_get_vblank_timestamp(). We can't just access
+	 * the hardware mode by e.g. looking at &drm_crtc_state.adjusted_mode,
 	 * because that one is really hard to get from interrupt context.
 	 */
 	struct drm_display_mode hwmode;
@@ -239,6 +239,10 @@  wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
 void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
 				   u32 max_vblank_count);
 
+/*
+ * Helpers for struct drm_crtc_funcs
+ */
+
 typedef bool (*drm_vblank_get_scanout_position_func)(struct drm_crtc *crtc,
 						     bool in_vblank_irq,
 						     int *vpos, int *hpos,
@@ -259,5 +263,9 @@  drm_crtc_vblank_helper_get_vblank_timestamp_internal(struct drm_crtc *crtc,
 						     bool in_vblank_irq,
 						     drm_vblank_get_scanout_position_func get_scanout_position,
 						     drm_vblank_get_scanout_position_legacy_func get_scanout_position_legacy);
+bool drm_crtc_vblank_helper_get_vblank_timestamp(struct drm_crtc *crtc,
+						 int *max_error,
+						 ktime_t *vblank_time,
+						 bool in_vblank_irq);
 
 #endif