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

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Message-ID: <608f95249ff3a39efb063ab9c6a543259a7b0ac9.camel@collabora.com>
Date: Thu, 05 Jun 2025 08:41:45 -0400
From: Nicolas Dufresne <nicolas.dufresne@...labora.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>, Hans Verkuil
	 <hans@...erkuil.nl>
Cc: 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 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.

Nicolas