Re: [PATCH v2 4/8] drm/xe: Use dma_fence_check_and_signal_locked()

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Dec 01, 2025 at 11:50:08AM +0100, Philipp Stanner wrote:
> Xe is one of the few users utilizing the return code of
> dma_fence_signal() to check whether a fence had already been signaled by
> someone else.
> 
> To clean up and simplify the dma_fence API, the few kernel users relying
> on that behavior shall be ported to an alternative function.
> 
> Replace dma_fence_signal_locked() with
> dma_fence_check_and_signal_locked().
> 
> Signed-off-by: Philipp Stanner <phasta@kernel.org>
> ---
>  drivers/gpu/drm/xe/xe_hw_fence.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_hw_fence.c b/drivers/gpu/drm/xe/xe_hw_fence.c
> index b2a0c46dfcd4..f6057456e460 100644
> --- a/drivers/gpu/drm/xe/xe_hw_fence.c
> +++ b/drivers/gpu/drm/xe/xe_hw_fence.c
> @@ -85,7 +85,6 @@ void xe_hw_fence_irq_finish(struct xe_hw_fence_irq *irq)
>  {
>  	struct xe_hw_fence *fence, *next;
>  	unsigned long flags;
> -	int err;
>  	bool tmp;
>  
>  	if (XE_WARN_ON(!list_empty(&irq->pending))) {
> @@ -93,9 +92,8 @@ void xe_hw_fence_irq_finish(struct xe_hw_fence_irq *irq)
>  		spin_lock_irqsave(&irq->lock, flags);
>  		list_for_each_entry_safe(fence, next, &irq->pending, irq_link) {
>  			list_del_init(&fence->irq_link);
> -			err = dma_fence_signal_locked(&fence->dma);
> +			XE_WARN_ON(dma_fence_check_and_signal_locked(&fence->dma));

I think XE_WARN_ON can compile out in certain builds. Best to leave warn on logic as is.

Also a little confused by this new helper... Doesn't
dma_fence_signal_locked already check if a fence is already signaled and
bail? Running out the door so I don't have time dig in here, but can you
explain?

Matt

>  			dma_fence_put(&fence->dma);
> -			XE_WARN_ON(err);
>  		}
>  		spin_unlock_irqrestore(&irq->lock, flags);
>  		dma_fence_end_signalling(tmp);
> -- 
> 2.49.0
>