Re: [PATCH 06/15] drm/panfrost: Fix implicit sync

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 22 Jun 2021 18:55:02 +0200
Daniel Vetter <daniel.vetter@ffwll.ch> wrote:

> Currently this has no practial relevance I think because there's not
> many who can pull off a setup with panfrost and another gpu in the
> same system. But the rules are that if you're setting an exclusive
> fence, indicating a gpu write access in the implicit fencing system,
> then you need to wait for all fences, not just the previous exclusive
> fence.
> 
> panfrost against itself has no problem, because it always sets the
> exclusive fence (but that's probably something that will need to be
> fixed for vulkan and/or multi-engine gpus, or you'll suffer badly).
> Also no problem with that against display.
> 
> With the prep work done to switch over to the dependency helpers this
> is now a oneliner.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: linux-media@vger.kernel.org
> Cc: linaro-mm-sig@lists.linaro.org
> ---
>  drivers/gpu/drm/panfrost/panfrost_job.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index 71cd43fa1b36..ef004d587dc4 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -203,9 +203,8 @@ static int panfrost_acquire_object_fences(struct drm_gem_object **bos,
>  	int i, ret;
>  
>  	for (i = 0; i < bo_count; i++) {
> -		struct dma_fence *fence = dma_resv_get_excl_unlocked(bos[i]->resv);
> -
> -		ret = drm_gem_fence_array_add(deps, fence);
> +		/* panfrost always uses write mode in its current uapi */
> +		ret = drm_gem_fence_array_add_implicit(deps, bos[i], true);
>  		if (ret)
>  			return ret;
>  	}