Patchwork [v3,1/6] drm/atomic: initial support for asynchronous plane update

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Submitter Gustavo F. Padovan
Date June 28, 2017, 8:54 p.m.
Message ID <20170628205500.8015-2-gustavo@padovan.org>
Download mbox | patch
Permalink /patch/9815499/
State New
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Comments

Gustavo F. Padovan - June 28, 2017, 8:54 p.m.
From: Gustavo Padovan <gustavo.padovan@collabora.com>

In some cases, like cursor updates, it is interesting to update the
plane in an asynchronous fashion to avoid big delays. The current queued
update could be still waiting for a fence to signal and thus block any
subsequent update until its scan out. In cases like this if we update the
cursor synchronously through the atomic API it will cause significant
delays that would even be noticed by the final user.

This patch creates a fast path to jump ahead the current queued state and
do single planes updates without going through all atomic steps in
drm_atomic_helper_commit(). We take this path for legacy cursor updates.

For now only single plane updates are supported, but we plan to support
multiple planes updates and async PageFlips through this interface as well
in the near future.

v5:
	- improve comments (Eric Anholt)

v4:
	- fix state->crtc NULL check (Archit Taneja)

v3:
	- fix iteration on the wrong crtc state
	- put back code to forbid updates if there is a queued update for
	the same plane (Ville Syrjälä)
	- move size checks back to drivers (Ville Syrjälä)
	- move ASYNC_UPDATE flag addition to its own patch (Ville Syrjälä)

v2:
	- allow updates even if there is a queued update for the same
	plane.
        - fixes on the documentation (Emil Velikov)
        - unconditionally call ->atomic_async_update (Emil Velikov)
        - check for ->atomic_async_update earlier (Daniel Vetter)
        - make ->atomic_async_check() the last step (Daniel Vetter)
        - add ASYNC_UPDATE flag (Eric Anholt)
        - update state in core after ->atomic_async_update (Eric Anholt)
	- update docs (Eric Anholt)

Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Acked-by: Eric Anholt <eric@anholt.net>
---
 drivers/gpu/drm/drm_atomic.c             | 70 ++++++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_atomic_helper.c      | 35 ++++++++++++++++
 include/drm/drm_atomic.h                 |  2 +
 include/drm/drm_atomic_helper.h          |  2 +
 include/drm/drm_modeset_helper_vtables.h | 50 +++++++++++++++++++++++
 5 files changed, 159 insertions(+)
Daniel Vetter - June 30, 2017, 7:30 a.m.
On Wed, Jun 28, 2017 at 05:54:55PM -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.com>
> 
> In some cases, like cursor updates, it is interesting to update the
> plane in an asynchronous fashion to avoid big delays. The current queued
> update could be still waiting for a fence to signal and thus block any
> subsequent update until its scan out. In cases like this if we update the
> cursor synchronously through the atomic API it will cause significant
> delays that would even be noticed by the final user.
> 
> This patch creates a fast path to jump ahead the current queued state and
> do single planes updates without going through all atomic steps in
> drm_atomic_helper_commit(). We take this path for legacy cursor updates.
> 
> For now only single plane updates are supported, but we plan to support
> multiple planes updates and async PageFlips through this interface as well
> in the near future.
> 
> v5:
> 	- improve comments (Eric Anholt)
> 
> v4:
> 	- fix state->crtc NULL check (Archit Taneja)
> 
> v3:
> 	- fix iteration on the wrong crtc state
> 	- put back code to forbid updates if there is a queued update for
> 	the same plane (Ville Syrjälä)
> 	- move size checks back to drivers (Ville Syrjälä)
> 	- move ASYNC_UPDATE flag addition to its own patch (Ville Syrjälä)
> 
> v2:
> 	- allow updates even if there is a queued update for the same
> 	plane.
>         - fixes on the documentation (Emil Velikov)
>         - unconditionally call ->atomic_async_update (Emil Velikov)
>         - check for ->atomic_async_update earlier (Daniel Vetter)
>         - make ->atomic_async_check() the last step (Daniel Vetter)
>         - add ASYNC_UPDATE flag (Eric Anholt)
>         - update state in core after ->atomic_async_update (Eric Anholt)
> 	- update docs (Eric Anholt)
> 
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Eric Anholt <eric@anholt.net>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
> Reviewed-by: Archit Taneja <architt@codeaurora.org>
> Acked-by: Eric Anholt <eric@anholt.net>

Ok I wanted to merge this, but found one more nit. The new
->atomic_async_commit/check hooks are imo driver interface functions (you
call the from the core drm_atomic.c), but you put the hooks into the
helper vtables. Can you pls move them into drm_plane_funcs instead?

The only reason this worked is because I accidentally left a
drm_plane_helper.h include in drm_atomic.c which shouldn't be there ...

Otherwise looks all good, and with that fix has my

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Thanks, Daniel

> ---
>  drivers/gpu/drm/drm_atomic.c             | 70 ++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_atomic_helper.c      | 35 ++++++++++++++++
>  include/drm/drm_atomic.h                 |  2 +
>  include/drm/drm_atomic_helper.h          |  2 +
>  include/drm/drm_modeset_helper_vtables.h | 50 +++++++++++++++++++++++
>  5 files changed, 159 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index c0f336d..e406688 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -644,6 +644,73 @@ static int drm_atomic_crtc_check(struct drm_crtc *crtc,
>  	return 0;
>  }
>  
> +static bool drm_atomic_async_check(struct drm_atomic_state *state)
> +{
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *crtc_state;
> +	struct drm_crtc_commit *commit;
> +	struct drm_plane *__plane, *plane = NULL;
> +	struct drm_plane_state *__plane_state, *plane_state = NULL;
> +	const struct drm_plane_helper_funcs *funcs;
> +	int i, j, n_planes = 0;
> +
> +	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
> +		if (drm_atomic_crtc_needs_modeset(crtc_state))
> +			return false;
> +	}
> +
> +	for_each_new_plane_in_state(state, __plane, __plane_state, i) {
> +		n_planes++;
> +		plane = __plane;
> +		plane_state = __plane_state;
> +	}
> +
> +	/* FIXME: we support only single plane updates for now */
> +	if (!plane || n_planes != 1)
> +		return false;
> +
> +	if (!plane_state->crtc)
> +		return false;
> +
> +	funcs = plane->helper_private;
> +	if (!funcs->atomic_async_update)
> +		return false;
> +
> +	if (plane_state->fence)
> +		return false;
> +
> +	/*
> +	 * Don't do an async update if there is an outstanding commit modifying
> +	 * the plane.  This prevents our async update's changes from getting
> +	 * overridden by a previous synchronous update's state.
> +	 */
> +	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
> +		if (plane->crtc != crtc)
> +			continue;
> +
> +		spin_lock(&crtc->commit_lock);
> +		commit = list_first_entry_or_null(&crtc->commit_list,
> +						  struct drm_crtc_commit,
> +						  commit_entry);
> +		if (!commit) {
> +			spin_unlock(&crtc->commit_lock);
> +			continue;
> +		}
> +		spin_unlock(&crtc->commit_lock);
> +
> +		if (!crtc->state->state)
> +			continue;
> +
> +		for_each_plane_in_state(crtc->state->state, __plane,
> +					__plane_state, j) {
> +			if (__plane == plane)
> +				return false;
> +		}
> +	}
> +
> +	return !funcs->atomic_async_check(plane, plane_state);
> +}
> +
>  static void drm_atomic_crtc_print_state(struct drm_printer *p,
>  		const struct drm_crtc_state *state)
>  {
> @@ -1665,6 +1732,9 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
>  		}
>  	}
>  
> +	if (state->legacy_cursor_update)
> +		state->async_update = drm_atomic_async_check(state);
> +
>  	return ret;
>  }
>  EXPORT_SYMBOL(drm_atomic_check_only);
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index c4e4e8b..8c4ee8b 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1346,6 +1346,30 @@ static void commit_work(struct work_struct *work)
>  }
>  
>  /**
> + * drm_atomic_helper_async_commit - commit state asynchronously
> + *
> + * This function commits a state asynchronously, i.e., not vblank
> + * synchronized. It should be used on a state only when
> + * drm_atomic_async_check() succeeds. Async commits are not supposed to swap
> + * the states like normal sync commits, but just do in-place changes on the
> + * current state.
> + */
> +void drm_atomic_helper_async_commit(struct drm_device *dev,
> +				    struct drm_atomic_state *state)
> +{
> +	struct drm_plane *plane;
> +	struct drm_plane_state *plane_state;
> +	const struct drm_plane_helper_funcs *funcs;
> +	int i;
> +
> +	for_each_new_plane_in_state(state, plane, plane_state, i) {
> +		funcs = plane->helper_private;
> +		funcs->atomic_async_update(plane, plane_state);
> +	}
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_async_commit);
> +
> +/**
>   * drm_atomic_helper_commit - commit validated state object
>   * @dev: DRM device
>   * @state: the driver state object
> @@ -1369,6 +1393,17 @@ int drm_atomic_helper_commit(struct drm_device *dev,
>  {
>  	int ret;
>  
> +	if (state->async_update) {
> +		ret = drm_atomic_helper_prepare_planes(dev, state);
> +		if (ret)
> +			return ret;
> +
> +		drm_atomic_helper_async_commit(dev, state);
> +		drm_atomic_helper_cleanup_planes(dev, state);
> +
> +		return 0;
> +	}
> +
>  	ret = drm_atomic_helper_setup_commit(state, nonblock);
>  	if (ret)
>  		return ret;
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 0196f26..dcc8e0c 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -207,6 +207,7 @@ struct __drm_private_objs_state {
>   * @dev: parent DRM device
>   * @allow_modeset: allow full modeset
>   * @legacy_cursor_update: hint to enforce legacy cursor IOCTL semantics
> + * @async_update: hint for asynchronous plane update
>   * @planes: pointer to array of structures with per-plane data
>   * @crtcs: pointer to array of CRTC pointers
>   * @num_connector: size of the @connectors and @connector_states arrays
> @@ -221,6 +222,7 @@ struct drm_atomic_state {
>  	struct drm_device *dev;
>  	bool allow_modeset : 1;
>  	bool legacy_cursor_update : 1;
> +	bool async_update : 1;
>  	struct __drm_planes_state *planes;
>  	struct __drm_crtcs_state *crtcs;
>  	int num_connector;
> diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> index 3bfeb2b..faa19fb 100644
> --- a/include/drm/drm_atomic_helper.h
> +++ b/include/drm/drm_atomic_helper.h
> @@ -44,6 +44,8 @@ void drm_atomic_helper_commit_tail(struct drm_atomic_state *state);
>  int drm_atomic_helper_commit(struct drm_device *dev,
>  			     struct drm_atomic_state *state,
>  			     bool nonblock);
> +void drm_atomic_helper_async_commit(struct drm_device *dev,
> +				    struct drm_atomic_state *state);
>  
>  int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
>  					struct drm_atomic_state *state,
> diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> index 474a102..2a83112 100644
> --- a/include/drm/drm_modeset_helper_vtables.h
> +++ b/include/drm/drm_modeset_helper_vtables.h
> @@ -1129,6 +1129,56 @@ struct drm_plane_helper_funcs {
>  	 */
>  	void (*atomic_disable)(struct drm_plane *plane,
>  			       struct drm_plane_state *old_state);
> +
> +	/**
> +	 * @atomic_async_check:
> +	 *
> +	 * Drivers should set this function pointer to check if the plane state
> +	 * can be updated in a async fashion. Here async means "not vblank
> +	 * synchronized".
> +	 *
> +	 * This hook is called by drm_atomic_async_check() to establish if a
> +	 * given update can be committed asynchronously, that is, if it can
> +	 * jump ahead of the state currently queued for update.
> +	 *
> +	 * RETURNS:
> +	 *
> +	 * Return 0 on success and any error returned indicates that the update
> +	 * can not be applied in asynchronous manner.
> +	 */
> +	int (*atomic_async_check)(struct drm_plane *plane,
> +				  struct drm_plane_state *state);
> +
> +	/**
> +	 * @atomic_async_update:
> +	 *
> +	 * Drivers should set this function pointer to perform asynchronous
> +	 * updates of planes, that is, jump ahead of the currently queued
> +	 * state and update the plane. Here async means "not vblank
> +	 * synchronized".
> +	 *
> +	 * This hook is called by drm_atomic_helper_async_commit().
> +	 *
> +	 * An async update will happen on legacy cursor updates. An async
> +	 * update won't happen if there is an outstanding commit modifying
> +	 * the same plane.
> +	 *
> +	 * Note that unlike &drm_plane_helper_funcs.atomic_update this hook
> +	 * takes the new &drm_plane_state as parameter. When doing async_update
> +	 * drivers shouldn't replace the &drm_plane_state but update the
> +	 * current one with the new plane configurations in the new
> +	 * plane_state.
> +	 *
> +	 * FIXME:
> +	 *  - It only works for single plane updates
> +	 *  - Async Pageflips are not supported yet
> +	 *  - Some hw might still scan out the old buffer until the next
> +	 *  vblank, however we let go of the fb references as soon as
> +	 *  we run this hook. For now drivers must implement their own workers
> +	 *  for deferring if needed, until a common solution is created.
> +	 */
> +	void (*atomic_async_update)(struct drm_plane *plane,
> +				    struct drm_plane_state *new_state);
>  };
>  
>  /**
> -- 
> 2.9.4
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
Daniel Vetter - June 30, 2017, 7:49 a.m.
On Fri, Jun 30, 2017 at 09:30:50AM +0200, Daniel Vetter wrote:
> On Wed, Jun 28, 2017 at 05:54:55PM -0300, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@collabora.com>
> > 
> > In some cases, like cursor updates, it is interesting to update the
> > plane in an asynchronous fashion to avoid big delays. The current queued
> > update could be still waiting for a fence to signal and thus block any
> > subsequent update until its scan out. In cases like this if we update the
> > cursor synchronously through the atomic API it will cause significant
> > delays that would even be noticed by the final user.
> > 
> > This patch creates a fast path to jump ahead the current queued state and
> > do single planes updates without going through all atomic steps in
> > drm_atomic_helper_commit(). We take this path for legacy cursor updates.
> > 
> > For now only single plane updates are supported, but we plan to support
> > multiple planes updates and async PageFlips through this interface as well
> > in the near future.
> > 
> > v5:
> > 	- improve comments (Eric Anholt)
> > 
> > v4:
> > 	- fix state->crtc NULL check (Archit Taneja)
> > 
> > v3:
> > 	- fix iteration on the wrong crtc state
> > 	- put back code to forbid updates if there is a queued update for
> > 	the same plane (Ville Syrjälä)
> > 	- move size checks back to drivers (Ville Syrjälä)
> > 	- move ASYNC_UPDATE flag addition to its own patch (Ville Syrjälä)
> > 
> > v2:
> > 	- allow updates even if there is a queued update for the same
> > 	plane.
> >         - fixes on the documentation (Emil Velikov)
> >         - unconditionally call ->atomic_async_update (Emil Velikov)
> >         - check for ->atomic_async_update earlier (Daniel Vetter)
> >         - make ->atomic_async_check() the last step (Daniel Vetter)
> >         - add ASYNC_UPDATE flag (Eric Anholt)
> >         - update state in core after ->atomic_async_update (Eric Anholt)
> > 	- update docs (Eric Anholt)
> > 
> > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Rob Clark <robdclark@gmail.com>
> > Cc: Eric Anholt <eric@anholt.net>
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
> > Reviewed-by: Archit Taneja <architt@codeaurora.org>
> > Acked-by: Eric Anholt <eric@anholt.net>
> 
> Ok I wanted to merge this, but found one more nit. The new
> ->atomic_async_commit/check hooks are imo driver interface functions (you
> call the from the core drm_atomic.c), but you put the hooks into the
> helper vtables. Can you pls move them into drm_plane_funcs instead?
> 
> The only reason this worked is because I accidentally left a
> drm_plane_helper.h include in drm_atomic.c which shouldn't be there ...

Otoh this does all feel supremely like helper code, so maybe the better
option would be to move all the code you're adding here into
drm_atomic_helper.c, (with function prefixes changed). You already call
async_commit from the helper's atomic_commit, and doing the same for the
check side would make things more symmetric.

I think that way round would be even cleaner separation between core code
and helpers.
-Daniel

> 
> Otherwise looks all good, and with that fix has my
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> Thanks, Daniel
> 
> > ---
> >  drivers/gpu/drm/drm_atomic.c             | 70 ++++++++++++++++++++++++++++++++
> >  drivers/gpu/drm/drm_atomic_helper.c      | 35 ++++++++++++++++
> >  include/drm/drm_atomic.h                 |  2 +
> >  include/drm/drm_atomic_helper.h          |  2 +
> >  include/drm/drm_modeset_helper_vtables.h | 50 +++++++++++++++++++++++
> >  5 files changed, 159 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index c0f336d..e406688 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -644,6 +644,73 @@ static int drm_atomic_crtc_check(struct drm_crtc *crtc,
> >  	return 0;
> >  }
> >  
> > +static bool drm_atomic_async_check(struct drm_atomic_state *state)
> > +{
> > +	struct drm_crtc *crtc;
> > +	struct drm_crtc_state *crtc_state;
> > +	struct drm_crtc_commit *commit;
> > +	struct drm_plane *__plane, *plane = NULL;
> > +	struct drm_plane_state *__plane_state, *plane_state = NULL;
> > +	const struct drm_plane_helper_funcs *funcs;
> > +	int i, j, n_planes = 0;
> > +
> > +	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
> > +		if (drm_atomic_crtc_needs_modeset(crtc_state))
> > +			return false;
> > +	}
> > +
> > +	for_each_new_plane_in_state(state, __plane, __plane_state, i) {
> > +		n_planes++;
> > +		plane = __plane;
> > +		plane_state = __plane_state;
> > +	}
> > +
> > +	/* FIXME: we support only single plane updates for now */
> > +	if (!plane || n_planes != 1)
> > +		return false;
> > +
> > +	if (!plane_state->crtc)
> > +		return false;
> > +
> > +	funcs = plane->helper_private;
> > +	if (!funcs->atomic_async_update)
> > +		return false;
> > +
> > +	if (plane_state->fence)
> > +		return false;
> > +
> > +	/*
> > +	 * Don't do an async update if there is an outstanding commit modifying
> > +	 * the plane.  This prevents our async update's changes from getting
> > +	 * overridden by a previous synchronous update's state.
> > +	 */
> > +	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
> > +		if (plane->crtc != crtc)
> > +			continue;
> > +
> > +		spin_lock(&crtc->commit_lock);
> > +		commit = list_first_entry_or_null(&crtc->commit_list,
> > +						  struct drm_crtc_commit,
> > +						  commit_entry);
> > +		if (!commit) {
> > +			spin_unlock(&crtc->commit_lock);
> > +			continue;
> > +		}
> > +		spin_unlock(&crtc->commit_lock);
> > +
> > +		if (!crtc->state->state)
> > +			continue;
> > +
> > +		for_each_plane_in_state(crtc->state->state, __plane,
> > +					__plane_state, j) {
> > +			if (__plane == plane)
> > +				return false;
> > +		}
> > +	}
> > +
> > +	return !funcs->atomic_async_check(plane, plane_state);
> > +}
> > +
> >  static void drm_atomic_crtc_print_state(struct drm_printer *p,
> >  		const struct drm_crtc_state *state)
> >  {
> > @@ -1665,6 +1732,9 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
> >  		}
> >  	}
> >  
> > +	if (state->legacy_cursor_update)
> > +		state->async_update = drm_atomic_async_check(state);
> > +
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(drm_atomic_check_only);
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index c4e4e8b..8c4ee8b 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -1346,6 +1346,30 @@ static void commit_work(struct work_struct *work)
> >  }
> >  
> >  /**
> > + * drm_atomic_helper_async_commit - commit state asynchronously
> > + *
> > + * This function commits a state asynchronously, i.e., not vblank
> > + * synchronized. It should be used on a state only when
> > + * drm_atomic_async_check() succeeds. Async commits are not supposed to swap
> > + * the states like normal sync commits, but just do in-place changes on the
> > + * current state.
> > + */
> > +void drm_atomic_helper_async_commit(struct drm_device *dev,
> > +				    struct drm_atomic_state *state)
> > +{
> > +	struct drm_plane *plane;
> > +	struct drm_plane_state *plane_state;
> > +	const struct drm_plane_helper_funcs *funcs;
> > +	int i;
> > +
> > +	for_each_new_plane_in_state(state, plane, plane_state, i) {
> > +		funcs = plane->helper_private;
> > +		funcs->atomic_async_update(plane, plane_state);
> > +	}
> > +}
> > +EXPORT_SYMBOL(drm_atomic_helper_async_commit);
> > +
> > +/**
> >   * drm_atomic_helper_commit - commit validated state object
> >   * @dev: DRM device
> >   * @state: the driver state object
> > @@ -1369,6 +1393,17 @@ int drm_atomic_helper_commit(struct drm_device *dev,
> >  {
> >  	int ret;
> >  
> > +	if (state->async_update) {
> > +		ret = drm_atomic_helper_prepare_planes(dev, state);
> > +		if (ret)
> > +			return ret;
> > +
> > +		drm_atomic_helper_async_commit(dev, state);
> > +		drm_atomic_helper_cleanup_planes(dev, state);
> > +
> > +		return 0;
> > +	}
> > +
> >  	ret = drm_atomic_helper_setup_commit(state, nonblock);
> >  	if (ret)
> >  		return ret;
> > diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> > index 0196f26..dcc8e0c 100644
> > --- a/include/drm/drm_atomic.h
> > +++ b/include/drm/drm_atomic.h
> > @@ -207,6 +207,7 @@ struct __drm_private_objs_state {
> >   * @dev: parent DRM device
> >   * @allow_modeset: allow full modeset
> >   * @legacy_cursor_update: hint to enforce legacy cursor IOCTL semantics
> > + * @async_update: hint for asynchronous plane update
> >   * @planes: pointer to array of structures with per-plane data
> >   * @crtcs: pointer to array of CRTC pointers
> >   * @num_connector: size of the @connectors and @connector_states arrays
> > @@ -221,6 +222,7 @@ struct drm_atomic_state {
> >  	struct drm_device *dev;
> >  	bool allow_modeset : 1;
> >  	bool legacy_cursor_update : 1;
> > +	bool async_update : 1;
> >  	struct __drm_planes_state *planes;
> >  	struct __drm_crtcs_state *crtcs;
> >  	int num_connector;
> > diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> > index 3bfeb2b..faa19fb 100644
> > --- a/include/drm/drm_atomic_helper.h
> > +++ b/include/drm/drm_atomic_helper.h
> > @@ -44,6 +44,8 @@ void drm_atomic_helper_commit_tail(struct drm_atomic_state *state);
> >  int drm_atomic_helper_commit(struct drm_device *dev,
> >  			     struct drm_atomic_state *state,
> >  			     bool nonblock);
> > +void drm_atomic_helper_async_commit(struct drm_device *dev,
> > +				    struct drm_atomic_state *state);
> >  
> >  int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
> >  					struct drm_atomic_state *state,
> > diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
> > index 474a102..2a83112 100644
> > --- a/include/drm/drm_modeset_helper_vtables.h
> > +++ b/include/drm/drm_modeset_helper_vtables.h
> > @@ -1129,6 +1129,56 @@ struct drm_plane_helper_funcs {
> >  	 */
> >  	void (*atomic_disable)(struct drm_plane *plane,
> >  			       struct drm_plane_state *old_state);
> > +
> > +	/**
> > +	 * @atomic_async_check:
> > +	 *
> > +	 * Drivers should set this function pointer to check if the plane state
> > +	 * can be updated in a async fashion. Here async means "not vblank
> > +	 * synchronized".
> > +	 *
> > +	 * This hook is called by drm_atomic_async_check() to establish if a
> > +	 * given update can be committed asynchronously, that is, if it can
> > +	 * jump ahead of the state currently queued for update.
> > +	 *
> > +	 * RETURNS:
> > +	 *
> > +	 * Return 0 on success and any error returned indicates that the update
> > +	 * can not be applied in asynchronous manner.
> > +	 */
> > +	int (*atomic_async_check)(struct drm_plane *plane,
> > +				  struct drm_plane_state *state);
> > +
> > +	/**
> > +	 * @atomic_async_update:
> > +	 *
> > +	 * Drivers should set this function pointer to perform asynchronous
> > +	 * updates of planes, that is, jump ahead of the currently queued
> > +	 * state and update the plane. Here async means "not vblank
> > +	 * synchronized".
> > +	 *
> > +	 * This hook is called by drm_atomic_helper_async_commit().
> > +	 *
> > +	 * An async update will happen on legacy cursor updates. An async
> > +	 * update won't happen if there is an outstanding commit modifying
> > +	 * the same plane.
> > +	 *
> > +	 * Note that unlike &drm_plane_helper_funcs.atomic_update this hook
> > +	 * takes the new &drm_plane_state as parameter. When doing async_update
> > +	 * drivers shouldn't replace the &drm_plane_state but update the
> > +	 * current one with the new plane configurations in the new
> > +	 * plane_state.
> > +	 *
> > +	 * FIXME:
> > +	 *  - It only works for single plane updates
> > +	 *  - Async Pageflips are not supported yet
> > +	 *  - Some hw might still scan out the old buffer until the next
> > +	 *  vblank, however we let go of the fb references as soon as
> > +	 *  we run this hook. For now drivers must implement their own workers
> > +	 *  for deferring if needed, until a common solution is created.
> > +	 */
> > +	void (*atomic_async_update)(struct drm_plane *plane,
> > +				    struct drm_plane_state *new_state);
> >  };
> >  
> >  /**
> > -- 
> > 2.9.4
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

Patch

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index c0f336d..e406688 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -644,6 +644,73 @@  static int drm_atomic_crtc_check(struct drm_crtc *crtc,
 	return 0;
 }
 
+static bool drm_atomic_async_check(struct drm_atomic_state *state)
+{
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc_commit *commit;
+	struct drm_plane *__plane, *plane = NULL;
+	struct drm_plane_state *__plane_state, *plane_state = NULL;
+	const struct drm_plane_helper_funcs *funcs;
+	int i, j, n_planes = 0;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		if (drm_atomic_crtc_needs_modeset(crtc_state))
+			return false;
+	}
+
+	for_each_new_plane_in_state(state, __plane, __plane_state, i) {
+		n_planes++;
+		plane = __plane;
+		plane_state = __plane_state;
+	}
+
+	/* FIXME: we support only single plane updates for now */
+	if (!plane || n_planes != 1)
+		return false;
+
+	if (!plane_state->crtc)
+		return false;
+
+	funcs = plane->helper_private;
+	if (!funcs->atomic_async_update)
+		return false;
+
+	if (plane_state->fence)
+		return false;
+
+	/*
+	 * Don't do an async update if there is an outstanding commit modifying
+	 * the plane.  This prevents our async update's changes from getting
+	 * overridden by a previous synchronous update's state.
+	 */
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		if (plane->crtc != crtc)
+			continue;
+
+		spin_lock(&crtc->commit_lock);
+		commit = list_first_entry_or_null(&crtc->commit_list,
+						  struct drm_crtc_commit,
+						  commit_entry);
+		if (!commit) {
+			spin_unlock(&crtc->commit_lock);
+			continue;
+		}
+		spin_unlock(&crtc->commit_lock);
+
+		if (!crtc->state->state)
+			continue;
+
+		for_each_plane_in_state(crtc->state->state, __plane,
+					__plane_state, j) {
+			if (__plane == plane)
+				return false;
+		}
+	}
+
+	return !funcs->atomic_async_check(plane, plane_state);
+}
+
 static void drm_atomic_crtc_print_state(struct drm_printer *p,
 		const struct drm_crtc_state *state)
 {
@@ -1665,6 +1732,9 @@  int drm_atomic_check_only(struct drm_atomic_state *state)
 		}
 	}
 
+	if (state->legacy_cursor_update)
+		state->async_update = drm_atomic_async_check(state);
+
 	return ret;
 }
 EXPORT_SYMBOL(drm_atomic_check_only);
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index c4e4e8b..8c4ee8b 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1346,6 +1346,30 @@  static void commit_work(struct work_struct *work)
 }
 
 /**
+ * drm_atomic_helper_async_commit - commit state asynchronously
+ *
+ * This function commits a state asynchronously, i.e., not vblank
+ * synchronized. It should be used on a state only when
+ * drm_atomic_async_check() succeeds. Async commits are not supposed to swap
+ * the states like normal sync commits, but just do in-place changes on the
+ * current state.
+ */
+void drm_atomic_helper_async_commit(struct drm_device *dev,
+				    struct drm_atomic_state *state)
+{
+	struct drm_plane *plane;
+	struct drm_plane_state *plane_state;
+	const struct drm_plane_helper_funcs *funcs;
+	int i;
+
+	for_each_new_plane_in_state(state, plane, plane_state, i) {
+		funcs = plane->helper_private;
+		funcs->atomic_async_update(plane, plane_state);
+	}
+}
+EXPORT_SYMBOL(drm_atomic_helper_async_commit);
+
+/**
  * drm_atomic_helper_commit - commit validated state object
  * @dev: DRM device
  * @state: the driver state object
@@ -1369,6 +1393,17 @@  int drm_atomic_helper_commit(struct drm_device *dev,
 {
 	int ret;
 
+	if (state->async_update) {
+		ret = drm_atomic_helper_prepare_planes(dev, state);
+		if (ret)
+			return ret;
+
+		drm_atomic_helper_async_commit(dev, state);
+		drm_atomic_helper_cleanup_planes(dev, state);
+
+		return 0;
+	}
+
 	ret = drm_atomic_helper_setup_commit(state, nonblock);
 	if (ret)
 		return ret;
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 0196f26..dcc8e0c 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -207,6 +207,7 @@  struct __drm_private_objs_state {
  * @dev: parent DRM device
  * @allow_modeset: allow full modeset
  * @legacy_cursor_update: hint to enforce legacy cursor IOCTL semantics
+ * @async_update: hint for asynchronous plane update
  * @planes: pointer to array of structures with per-plane data
  * @crtcs: pointer to array of CRTC pointers
  * @num_connector: size of the @connectors and @connector_states arrays
@@ -221,6 +222,7 @@  struct drm_atomic_state {
 	struct drm_device *dev;
 	bool allow_modeset : 1;
 	bool legacy_cursor_update : 1;
+	bool async_update : 1;
 	struct __drm_planes_state *planes;
 	struct __drm_crtcs_state *crtcs;
 	int num_connector;
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 3bfeb2b..faa19fb 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -44,6 +44,8 @@  void drm_atomic_helper_commit_tail(struct drm_atomic_state *state);
 int drm_atomic_helper_commit(struct drm_device *dev,
 			     struct drm_atomic_state *state,
 			     bool nonblock);
+void drm_atomic_helper_async_commit(struct drm_device *dev,
+				    struct drm_atomic_state *state);
 
 int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
 					struct drm_atomic_state *state,
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 474a102..2a83112 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -1129,6 +1129,56 @@  struct drm_plane_helper_funcs {
 	 */
 	void (*atomic_disable)(struct drm_plane *plane,
 			       struct drm_plane_state *old_state);
+
+	/**
+	 * @atomic_async_check:
+	 *
+	 * Drivers should set this function pointer to check if the plane state
+	 * can be updated in a async fashion. Here async means "not vblank
+	 * synchronized".
+	 *
+	 * This hook is called by drm_atomic_async_check() to establish if a
+	 * given update can be committed asynchronously, that is, if it can
+	 * jump ahead of the state currently queued for update.
+	 *
+	 * RETURNS:
+	 *
+	 * Return 0 on success and any error returned indicates that the update
+	 * can not be applied in asynchronous manner.
+	 */
+	int (*atomic_async_check)(struct drm_plane *plane,
+				  struct drm_plane_state *state);
+
+	/**
+	 * @atomic_async_update:
+	 *
+	 * Drivers should set this function pointer to perform asynchronous
+	 * updates of planes, that is, jump ahead of the currently queued
+	 * state and update the plane. Here async means "not vblank
+	 * synchronized".
+	 *
+	 * This hook is called by drm_atomic_helper_async_commit().
+	 *
+	 * An async update will happen on legacy cursor updates. An async
+	 * update won't happen if there is an outstanding commit modifying
+	 * the same plane.
+	 *
+	 * Note that unlike &drm_plane_helper_funcs.atomic_update this hook
+	 * takes the new &drm_plane_state as parameter. When doing async_update
+	 * drivers shouldn't replace the &drm_plane_state but update the
+	 * current one with the new plane configurations in the new
+	 * plane_state.
+	 *
+	 * FIXME:
+	 *  - It only works for single plane updates
+	 *  - Async Pageflips are not supported yet
+	 *  - Some hw might still scan out the old buffer until the next
+	 *  vblank, however we let go of the fb references as soon as
+	 *  we run this hook. For now drivers must implement their own workers
+	 *  for deferring if needed, until a common solution is created.
+	 */
+	void (*atomic_async_update)(struct drm_plane *plane,
+				    struct drm_plane_state *new_state);
 };
 
 /**