Re: [PATCH] drm/atomic-helper: Simplify commit tracking locking

[Sean Paul <seanpaul@chromium.org>]

On Wed, Jun 21, 2017 at 11:16:27AM +0200, Daniel Vetter wrote:
> The crtc->commit_lock only protects commit_list and commit_entry. If
> we chase the pointer from the drm_atomic_state update structure, then
> we don't need any locks (since we hold a reference already).
> 
> Simplify the locking accordingly.
> 
> Noticed while reviewing a patch from Boris.
> 
> Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

After reading this over a few times, I've convinced myself that it does
the right thing.

Reviewed-by: Sean Paul <seanpaul@chromium.org>


> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 86d3093c6c9b..9bf86eb87fe1 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1680,9 +1680,7 @@ void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *old_state)
>  
>  		/* backend must have consumed any event by now */
>  		WARN_ON(new_crtc_state->event);
> -		spin_lock(&crtc->commit_lock);
>  		complete_all(&commit->hw_done);
> -		spin_unlock(&crtc->commit_lock);
>  	}
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_commit_hw_done);
> @@ -1711,7 +1709,6 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
>  		if (WARN_ON(!commit))
>  			continue;
>  
> -		spin_lock(&crtc->commit_lock);
>  		complete_all(&commit->cleanup_done);
>  		WARN_ON(!try_wait_for_completion(&commit->hw_done));
>  
> @@ -1721,8 +1718,6 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
>  		if (try_wait_for_completion(&commit->flip_done))
>  			goto del_commit;
>  
> -		spin_unlock(&crtc->commit_lock);
> -
>  		/* 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. */
> @@ -1732,8 +1727,8 @@ void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *old_state)
>  			DRM_ERROR("[CRTC:%d:%s] flip_done timed out\n",
>  				  crtc->base.id, crtc->name);
>  
> -		spin_lock(&crtc->commit_lock);
>  del_commit:
> +		spin_lock(&crtc->commit_lock);
>  		list_del(&commit->commit_entry);
>  		spin_unlock(&crtc->commit_lock);
>  	}
> -- 
> 2.11.0
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS
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