Re: [PATCH 11/24] drm/amdgpu: use dma_resv_for_each_fence for CS workaround

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Dec 07, 2021 at 01:33:58PM +0100, Christian König wrote:
> Get the write fence using dma_resv_for_each_fence instead of accessing
> it manually.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> index 53e407ea4c89..7facd614e50a 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> @@ -1268,6 +1268,8 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p,
>  	amdgpu_bo_list_for_each_entry(e, p->bo_list) {
>  		struct dma_resv *resv = e->tv.bo->base.resv;
>  		struct dma_fence_chain *chain = e->chain;
> +		struct dma_resv_iter cursor;
> +		struct dma_fence *fence;
>  
>  		if (!chain)
>  			continue;
> @@ -1277,9 +1279,10 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p,
>  		 * submission in a dma_fence_chain and add it as exclusive
>  		 * fence.
>  		 */
> -		dma_fence_chain_init(chain, dma_resv_excl_fence(resv),
> -				     dma_fence_get(p->fence), 1);
> -
> +		dma_resv_for_each_fence(&cursor, resv, false, fence) {
> +			break;
> +		}
> +		dma_fence_chain_init(chain, fence, dma_fence_get(p->fence), 1);

Uh this needs a TODO. I'm assuming you'll fix this up later on when
there's more than write fence, but in case of bisect or whatever this is a
bit too clever. Like you just replace one "dig around in dma-resv
implementation details" with one that's not even a documented interface
:-)

With an adequately loud comment added interim:

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

>  		rcu_assign_pointer(resv->fence_excl, &chain->base);
>  		e->chain = NULL;
>  	}
> -- 
> 2.25.1
> 

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