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

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Message-ID: <aS8MWTnmjmEkn6YG@lstrano-desk.jf.intel.com>
Date: Tue, 2 Dec 2025 07:57:13 -0800
From: Matthew Brost <matthew.brost@...el.com>
To: <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 Tue, Dec 02, 2025 at 08:17:17AM +0100, Philipp Stanner wrote:
> 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.
> 

Thanks for explaination. This should work then with XE_WARN_ON refactor.

Matt

> 
> 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
> > > 
>