[PATCH 2/5] drm/atomic: Remove waits in drm_atomic_helper_commit_cleanup_done

[Daniel Vetter]

On Wed, Aug 30, 2017 at 02:17:49PM +0200, Maarten Lankhorst wrote:
> When commit synchronization through drm_crtc_commit was first
> introduced, we tried to solve the problem of the flip_done
> needing a reference count by blocking in cleanup_done.
> 
> This has been changed by commit 24835e442f28 ("drm: reference count
> event->completion") which made the waits here no longer needed.

This is wrong. Your next patch makes this no longer necessary.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 17 -----------------
>  1 file changed, 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 4e53aae9a1fb..11d0e94a2181 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1885,7 +1885,6 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
>  	struct drm_crtc_state *new_crtc_state;
>  	struct drm_crtc_commit *commit;
>  	int i;
> -	long ret;
>  
>  	for_each_new_crtc_in_state(old_state, crtc, new_crtc_state, i) {
>  		commit = old_state->crtcs[i].commit;
> @@ -1895,22 +1894,6 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
>  		complete_all(&commit->cleanup_done);
>  		WARN_ON(!try_wait_for_completion(&commit->hw_done));
>  
> -		/* commit_list borrows our reference, need to remove before we
> -		 * clean up our drm_atomic_state. But only after it actually
> -		 * completed, otherwise subsequent commits won't stall properly. */

This comment here is the clue: "... otherwise subsequent commits wont
stall properly". When we remove the drm_crtc_commit from commit_list, the
next commit won't be able to properly stall for flip_done. Hence we must
wait for flip_done before removing it.

But with your new patch we wait for flip_done using
old_crtc_state->commit, and this is indeed no longer necessary.

With the commit message and patch ordering fixed up:

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

> -		if (try_wait_for_completion(&commit->flip_done))
> -			goto del_commit;
> -
> -		/* We must wait for the vblank event to signal our completion
> -		 * before releasing our reference, since the vblank work does
> -		 * not hold a reference of its own. */
> -		ret = wait_for_completion_timeout(&commit->flip_done,
> -						  10*HZ);
> -		if (ret == 0)
> -			DRM_ERROR("[CRTC:%d:%s] flip_done timed out\n",
> -				  crtc->base.id, crtc->name);
> -
> -del_commit:
>  		spin_lock(&crtc->commit_lock);
>  		list_del(&commit->commit_entry);
>  		spin_unlock(&crtc->commit_lock);
> -- 
> 2.11.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch