Re: [PATCH 19/26] drm: support more than one write fence in drm_gem_plane_helper_prepare_fb

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Nov 23, 2021 at 03:21:04PM +0100, Christian König wrote:
> Use dma_resv_get_singleton() here to eventually get more than one write
> fence as single fence.

Yeah this is nice, atomic commit helpers not supporting multiple write
fences was really my main worry in this entire endeavour. Otherwise looks
all rather reasonable.

I'll try to find some review bandwidth, but would be really if you can
volunteer others too (especially making sure ttm drivers set the KERNEL
fences correctly in all cases).
-Daniel


> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/gpu/drm/drm_gem_atomic_helper.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_atomic_helper.c b/drivers/gpu/drm/drm_gem_atomic_helper.c
> index c3189afe10cb..9338ddb7edff 100644
> --- a/drivers/gpu/drm/drm_gem_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_gem_atomic_helper.c
> @@ -143,25 +143,21 @@
>   */
>  int drm_gem_plane_helper_prepare_fb(struct drm_plane *plane, struct drm_plane_state *state)
>  {
> -	struct dma_resv_iter cursor;
>  	struct drm_gem_object *obj;
>  	struct dma_fence *fence;
> +	int ret;
>  
>  	if (!state->fb)
>  		return 0;
>  
>  	obj = drm_gem_fb_get_obj(state->fb, 0);
> -	dma_resv_iter_begin(&cursor, obj->resv, false);
> -	dma_resv_for_each_fence_unlocked(&cursor, fence) {
> -		/* TODO: Currently there should be only one write fence, so this
> -		 * here works fine. But drm_atomic_set_fence_for_plane() should
> -		 * be changed to be able to handle more fences in general for
> -		 * multiple BOs per fb anyway. */
> -		dma_fence_get(fence);
> -		break;
> -	}
> -	dma_resv_iter_end(&cursor);
> +	ret = dma_resv_get_singleton(obj->resv, false, &fence);
> +	if (ret)
> +		return ret;
>  
> +	/* TODO: drm_atomic_set_fence_for_plane() should be changed to be able
> +	 * to handle more fences in general for multiple BOs per fb.
> +	 */
>  	drm_atomic_set_fence_for_plane(state, fence);
>  	return 0;
>  }
> -- 
> 2.25.1
> 

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