Re: [RFC] drm/atomic+msm: add helper to implement legacy dirtyfb

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 03, 2018 at 06:42:23PM -0400, Rob Clark wrote:
> Add an atomic helper to implement dirtyfb support.  This is needed to
> support DSI command-mode panels with x11 userspace (ie. when we can't
> rely on pageflips to trigger a flush to the panel).
> 
> To signal to the driver that the async atomic update needs to
> synchronize with fences, even though the fb didn't change, the
> drm_atomic_state::dirty flag is added.
> 
> Signed-off-by: Rob Clark <robdclark@gmail.com>
> ---
> Background: there are a number of different folks working on getting
> upstream kernel working on various different phones/tablets with qcom
> SoC's.. many of them have command mode panels, so we kind of need a
> way to support the legacy dirtyfb ioctl for x11 support.
> 
> I know there is work on a proprer non-legacy atomic property for
> userspace to communicate dirty-rect(s) to the kernel, so this can
> be improved from triggering a full-frame flush once that is in
> place.  But we kinda needa a stop-gap solution.
> 
> I had considered an in-driver solution for this, but things get a
> bit tricky if userspace ands up combining dirtyfb ioctls with page-
> flips, because we need to synchronize setting various CTL.FLUSH bits
> with setting the CTL.START bit.  (ie. really all we need to do for
> cmd mode panels is bang CTL.START, but is this ends up racing with
> pageflips setting FLUSH bits, then bad things.)  The easiest soln
> is to wrap this up as an atomic commit and rely on the worker to
> serialize things.  Hence adding an atomic dirtyfb helper.
> 
> I guess at least the helper, with some small addition to translate
> and pass-thru the dirty rect(s) is useful to the final atomic dirty-
> rect property solution.  Depending on how far off that is, a stop-
> gap solution could be useful.
> 
>  drivers/gpu/drm/drm_atomic_helper.c | 66 +++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/msm/msm_atomic.c    |  5 ++-
>  drivers/gpu/drm/msm/msm_fb.c        |  1 +
>  include/drm/drm_atomic_helper.h     |  4 +++
>  include/drm/drm_plane.h             |  9 +++++
>  5 files changed, 84 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index c35654591c12..a578dc681b27 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3504,6 +3504,7 @@ void __drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
>  	if (state->fb)
>  		drm_framebuffer_get(state->fb);
>  
> +	state->dirty = false;
>  	state->fence = NULL;
>  	state->commit = NULL;
>  }
> @@ -3847,6 +3848,71 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_legacy_gamma_set);
>  
> +/**
> + * drm_atomic_helper_dirtyfb - helper for dirtyfb
> + *
> + * A helper to implement drm_framebuffer_funcs::dirty
> + */
> +int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
> +			      struct drm_file *file_priv, unsigned flags,
> +			      unsigned color, struct drm_clip_rect *clips,
> +			      unsigned num_clips)
> +{
> +	struct drm_modeset_acquire_ctx ctx;
> +	struct drm_atomic_state *state;
> +	struct drm_plane *plane;
> +	int ret = 0;
> +
> +	/*
> +	 * When called from ioctl, we are interruptable, but not when
> +	 * called internally (ie. defio worker)
> +	 */
> +	drm_modeset_acquire_init(&ctx,
> +		file_priv ? DRM_MODESET_ACQUIRE_INTERRUPTIBLE : 0);
> +
> +	state = drm_atomic_state_alloc(fb->dev);
> +	if (!state) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +	state->acquire_ctx = &ctx;
> +
> +retry:
> +	drm_for_each_plane(plane, fb->dev) {
> +		struct drm_plane_state *plane_state;
> +
> +		if (plane->state->fb != fb)
> +			continue;
> +
> +		plane_state = drm_atomic_get_plane_state(state, plane);
> +		if (IS_ERR(plane_state)) {
> +			ret = PTR_ERR(plane_state);
> +			goto out;
> +		}
> +
> +		plane_state->dirty = true;
> +	}
> +
> +	ret = drm_atomic_nonblocking_commit(state);
> +
> +out:
> +	if (ret == -EDEADLK) {
> +		drm_atomic_state_clear(state);
> +		ret = drm_modeset_backoff(&ctx);
> +		if (!ret)
> +			goto retry;
> +	}
> +
> +	drm_atomic_state_put(state);
> +
> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +
> +	return ret;
> +
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_dirtyfb);
> +
>  /**
>   * __drm_atomic_helper_private_duplicate_state - copy atomic private state
>   * @obj: CRTC object
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
> index bf5f8c39f34d..bb55a048e98b 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -201,7 +201,10 @@ int msm_atomic_commit(struct drm_device *dev,
>  	 * Figure out what fence to wait for:
>  	 */
>  	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
> -		if ((new_plane_state->fb != old_plane_state->fb) && new_plane_state->fb) {
> +		bool sync_fb = new_plane_state->fb &&
> +			((new_plane_state->fb != old_plane_state->fb) ||
> +			 new_plane_state->dirty);

Why do you have this optimization even here? Imo flipping to the same fb
should result in the fb getting fully uploaded, whether you're doing a
legacy page_flip, and atomic one or just a plane update.

Iirc some userspace does use that as essentially a full-plane frontbuffer
rendering flush already. IOW I don't think we need your
plane_state->dirty, it's implied to always be true - why would userspace
do a flip otherwise?

The helper itself to map dirtyfb to a nonblocking atomic commit looks
reasonable, but misses a bunch of the trickery discussed with Noralf and
others I think.
-Daniel

> +		if (sync_fb) {
>  			struct drm_gem_object *obj = msm_framebuffer_bo(new_plane_state->fb, 0);
>  			struct msm_gem_object *msm_obj = to_msm_bo(obj);
>  			struct dma_fence *fence = reservation_object_get_excl_rcu(msm_obj->resv);
> diff --git a/drivers/gpu/drm/msm/msm_fb.c b/drivers/gpu/drm/msm/msm_fb.c
> index 0e0c87252ab0..a5d882a34a33 100644
> --- a/drivers/gpu/drm/msm/msm_fb.c
> +++ b/drivers/gpu/drm/msm/msm_fb.c
> @@ -62,6 +62,7 @@ static void msm_framebuffer_destroy(struct drm_framebuffer *fb)
>  static const struct drm_framebuffer_funcs msm_framebuffer_funcs = {
>  	.create_handle = msm_framebuffer_create_handle,
>  	.destroy = msm_framebuffer_destroy,
> +	.dirty = drm_atomic_helper_dirtyfb,
>  };
>  
>  #ifdef CONFIG_DEBUG_FS
> diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> index 26aaba58d6ce..9b7a95c2643d 100644
> --- a/include/drm/drm_atomic_helper.h
> +++ b/include/drm/drm_atomic_helper.h
> @@ -183,6 +183,10 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>  				       u16 *red, u16 *green, u16 *blue,
>  				       uint32_t size,
>  				       struct drm_modeset_acquire_ctx *ctx);
> +int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
> +			      struct drm_file *file_priv, unsigned flags,
> +			      unsigned color, struct drm_clip_rect *clips,
> +			      unsigned num_clips);
>  void __drm_atomic_helper_private_obj_duplicate_state(struct drm_private_obj *obj,
>  						     struct drm_private_state *state);
>  
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index f7bf4a48b1c3..296fa22bda7a 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -76,6 +76,15 @@ struct drm_plane_state {
>  	 */
>  	struct drm_framebuffer *fb;
>  
> +	/**
> +	 * @dirty:
> +	 *
> +	 * Flag that indicates the fb contents have changed even though the
> +	 * fb has not.  This is mostly a stop-gap solution until we have
> +	 * atomic dirty-rect(s) property.
> +	 */
> +	bool dirty;
> +
>  	/**
>  	 * @fence:
>  	 *
> -- 
> 2.14.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch