linux-kernel - Re: [PATCH v2 4/8] drm/xe: Use dma_fence_check_and_signal

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Message-ID: <e2799662727a10b77b77ceb2fc2cdabe27537e3e.camel@mailbox.org>
Date: Tue, 02 Dec 2025 08:17:17 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: Matthew Brost <matthew.brost@...el.com>, Philipp Stanner
 <phasta@...nel.org>
Cc: Sumit Semwal <sumit.semwal@...aro.org>, Gustavo Padovan
 <gustavo@...ovan.org>, Christian König
 <christian.koenig@....com>, Felix Kuehling <Felix.Kuehling@....com>, Alex
 Deucher <alexander.deucher@....com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi
 <rodrigo.vivi@...el.com>,  Tvrtko Ursulin <tursulin@...ulin.net>, Huang Rui
 <ray.huang@....com>, Matthew Auld <matthew.auld@...el.com>,  Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, Lucas De
 Marchi <lucas.demarchi@...el.com>, Thomas Hellström
 <thomas.hellstrom@...ux.intel.com>, linux-media@...r.kernel.org,
 dri-devel@...ts.freedesktop.org,  linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org,  intel-gfx@...ts.freedesktop.org,
 intel-xe@...ts.freedesktop.org
Subject: Re: [PATCH v2 4/8] drm/xe: Use dma_fence_check_and_signal_locked()

On Mon, 2025-12-01 at 11:38 -0800, Matthew Brost wrote:
> 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@...nel.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.

OK, will adjust.

> 
> 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?

Yes, that is what dma_fence_signal_locked() *currently* does. The
series, however, is about removing that check from the default
interfaces because barely anyone uses dma_fence_signal() et.al.'s
return code. To simplify the interfaces.
The 2-3 users who need the code get this new function. See cover
letter.


P.

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