linux-kernel - Re: [PATCH 4/4] drm/nouveau: Check dma

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Message-ID: <9793bfc7-5309-4e19-a0e4-5e298720aa9e@amd.com>
Date: Mon, 28 Apr 2025 16:45:51 +0200
From: Christian König <christian.koenig@....com>
To: Philipp Stanner <phasta@...nel.org>, Lyude Paul <lyude@...hat.com>,
 Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Sumit Semwal <sumit.semwal@...aro.org>
Cc: dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH 4/4] drm/nouveau: Check dma_fence in canonical way

On 4/24/25 15:02, Philipp Stanner wrote:
> In nouveau_fence_done(), a fence is checked for being signaled by
> manually evaluating the base fence's bits. This can be done in a
> canonical manner through dma_fence_is_signaled().
> 
> Replace the bit-check with dma_fence_is_signaled().
> 
> Signed-off-by: Philipp Stanner <phasta@...nel.org>


I think the bit check was used here as fast path optimization because we later call dma_fence_is_signaled() anyway.

Feel free to add my acked-by, but honestly what nouveau does here looks rather suspicious to me.

Regards,
Christian.

> ---
>  drivers/gpu/drm/nouveau/nouveau_fence.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index fb9811938c82..d5654e26d5bc 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -253,7 +253,7 @@ nouveau_fence_done(struct nouveau_fence *fence)
>  	struct nouveau_channel *chan;
>  	unsigned long flags;
>  
> -	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->base.flags))
> +	if (dma_fence_is_signaled(&fence->base))
>  		return true;
>  
>  	spin_lock_irqsave(&fctx->lock, flags);