Re: [PATCH 07/25] drm/komdea: Annotate dma-fence critical section in commit path

["james qian wang (Arm Technology China)" <james.qian.wang@arm.com>]

On Tue, Jul 07, 2020 at 10:12:11PM +0200, Daniel Vetter wrote:
> Like the helpers, nothing special. Well except not, because we the
> critical section extends until after hw_done(), since that's the last
> thing which could hold up a subsequent atomic commit. That means the
> wait_for_flip_done is included, but that's not a problem, we're
> allowed to call dma_fence_wait() from signalling critical sections.
> Even on our own fence (which this does), it's just a bit confusing.
> But in a way those last 2 function calls are already part of the fence
> signalling critical section for the next atomic commit.
> 
> Reading this I'm wondering why komeda waits for flip_done() before
> calling hw_done(), which is a bit backwards (but hey hw can be
> special). Might be good to throw a comment in there that explains why,
> because the original commit that added this just doesn't.

Hi Daniel:

It's a typo, thank you for pointing this out, and I'll give a fix after
this series have been merged.

for this patch

Reviewed-by: James Qian Wang <james.qian.wang@arm.com>

> Cc: "James (Qian) Wang" <james.qian.wang@arm.com>
> Cc: Liviu Dudau <liviu.dudau@arm.com>
> Cc: Mihail Atanassov <mihail.atanassov@arm.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_kms.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> index 1f6682032ca4..cc5b5915bc5e 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> @@ -73,6 +73,7 @@ static struct drm_driver komeda_kms_driver = {
>  static void komeda_kms_commit_tail(struct drm_atomic_state *old_state)
>  {
>  	struct drm_device *dev = old_state->dev;
> +	bool fence_cookie = dma_fence_begin_signalling();
>  
>  	drm_atomic_helper_commit_modeset_disables(dev, old_state);
>  
> @@ -85,6 +86,8 @@ static void komeda_kms_commit_tail(struct drm_atomic_state *old_state)
>  
>  	drm_atomic_helper_commit_hw_done(old_state);
>  
> +	dma_fence_end_signalling(fence_cookie);
> +
>  	drm_atomic_helper_cleanup_planes(dev, old_state);
>  }
>  
> -- 
> 2.27.0