linux-kernel - Re: [PATCH 2/6] gpu: host1x: Fix syncpoint wait return value

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Date:	Tue, 11 Jun 2013 12:48:01 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Keith Packard <keithp@...thp.com>
Cc:	Arto Merilainen <amerilainen@...dia.com>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Terje Bergstrom <tbergstrom@...dia.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	xorg-devel@...ts.x.org
Subject: Re: [PATCH 2/6] gpu: host1x: Fix syncpoint wait return value

On Tue, May 28, 2013 at 01:12:12PM -0600, Keith Packard wrote:
> Thierry Reding <thierry.reding@...il.com> writes:
> 
> 
> > That doesn't sound right. Maybe drmIoctl() needs fixing instead. Looking
> > at the history, drmIoctl() was introduced to automatically loop if a
> > signal was received (commit 8b9ab108ec1f2ba2b503f713769c4946849b3cb2).
> > However the ioctl(3p) manpage doesn't mention that ioctl() returns
> > EAGAIN in case it is interrupted by a signal.
> 
> EAGAIN is being returned when the GPU is wedged to ask the application
> to re-submit the request, which will presumably be held until the  GPU
> is un-wedged.

Isn't that a bit risky? What if something special needs to be done to
unwedge the GPU other than re-submit the request, or if it just can't
be reasonably unwedged. In that case drmIoctl() will keep looping
indefinitely.

If the above is indeed the expected behaviour for drivers, then we need
a different error code for the SYNCPT_WAIT ioctl. EAGAIN is the best fit
and anything else doesn't quite match the use-case. A different option
might be not to use drmIoctl() on Tegra.

Thierry

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