linux-kernel - Re: [PATCH 5.10 079/126] drm/tegra: sor: Grab runtime PM reference across reset

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Message-ID: <20210406191452.GA25862@amd>
Date:   Tue, 6 Apr 2021 21:14:53 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Thierry Reding <treding@...dia.com>
Cc:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jonathan Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH 5.10 079/126] drm/tegra: sor: Grab runtime PM reference
 across reset

Hi!

> > > However, these functions alone don't provide any guarantees at the
> > > system level. Drivers need to ensure that the only a single consumer has
> > > access to the reset at the same time. In order for the SOR to be able to
> > > exclusively access its reset, it must therefore ensure that the SOR
> > > power domain is not powered off by holding on to a runtime PM reference
> > > to that power domain across the reset assert/deassert operation.
> > 
> > Yeah, but it should not leak the PM reference in the error handling.
> 
> True. However the only reason why the code could realistically fail
> between pm_runtime_resume_and_get() and pm_runtime_put() is if we did
> not take the runtime PM reference (which would cause the call to
> reset_control_acquire() to fail).
> 
> So the chances of this actually leaking are practically zero, so I
> didn't want to bloat this bugfix with what's essentially dead code. I
> can queue up your fix below for v5.14, though, since it's obviously
> more correct from a theoretical point of view.

Yes, that sounds like good solution, thanks!

Best regards,
								Pavel

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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