linux-kernel - Re: [PATCH v3 1/5] media: mc: add manual request completion

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Message-ID: <aEasmfi3VBkuFU3g@kekkonen.localdomain>
Date: Mon, 9 Jun 2025 09:42:49 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Nicolas Dufresne <nicolas.dufresne@...labora.com>
Cc: Hans Verkuil <hans@...erkuil.nl>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Tiffany Lin <tiffany.lin@...iatek.com>,
	Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
	Yunfei Dong <yunfei.dong@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, kernel@...labora.com,
	linux-media@...r.kernel.org,
	Sebastian Fricke <sebastian.fricke@...labora.com>
Subject: Re: [PATCH v3 1/5] media: mc: add manual request completion

Hi,

On Thu, Jun 05, 2025 at 08:41:45AM -0400, Nicolas Dufresne wrote:
> Hi Hans, Sakari,
> 
> Le jeudi 05 juin 2025 à 09:48 +0000, Sakari Ailus a écrit :
> > > It's not user-triggerable, if this happens, then it is a driver bug.
> > 
> > If there is a driver bug, it could well be user-triggerable, wouldn't it?
> > Testing may not uncover all such cases.
> 
> You are both right, if the driver is not used, the warning will never
> trigger. I was worried of the hit of a thread safe ONCE implementation,
> but WARN_ONCE is simply not, it can warn few time before it stops if
> called from multiple CPUs at the same time. In that specific function,
> I can move all the checks inside the lock to make it truly once.
> 
> Now its up to you, I don't have strong preference. These are driver errors,
> and usually quite critical. They are not bug_on simply because we have a
> crash free resolution, but its probably not functional anymore.

I'd prefer _ONCE variants, I wonder what Hans thinks.

-- 
Regards,

Sakari Ailus