linux-kernel - Re: [PATCH] drm/nouveau: handle -EACCES runtime PM return code

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Date:	Mon, 10 Feb 2014 13:34:25 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Ben Skeggs <bskeggs@...hat.com>, nouveau@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	gnurou@...il.com
Subject: Re: [PATCH] drm/nouveau: handle -EACCES runtime PM return code

On Mon, Feb 10, 2014 at 02:58:12PM +0900, Alexandre Courbot wrote:
> pm_runtime_get*() may return -EACCESS to indicate a device does not have

s/-EACCESS/-EACCES/

> runtime PM enabled. This is the case when the nouveau.runpm parameter is
> set to 0, and is not an error in that context. Handle this case without
> failure.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  drivers/gpu/drm/nouveau/dispnv04/crtc.c     | 2 +-
>  drivers/gpu/drm/nouveau/nouveau_connector.c | 2 +-
>  drivers/gpu/drm/nouveau/nouveau_drm.c       | 4 ++--
>  3 files changed, 4 insertions(+), 4 deletions(-)

I'm not sure if the commit message is entirely accurate. Looking at the
various runtime power-management functions in nouveau_drm.c (such as
nouveau_pmops_runtime_suspend() for example), they seem to return
-EINVAL if the nouveau.runpm parameter is set to 0.

However it seems like -EACCES is indeed returned when runtime power-
management hasn't been enabled for a device. This is done automatically
for PCI devices, but not for platform devices. We don't support runtime
power-management on gk20a yet, therefore pm_runtime_enable() is never
called, causing disable_depth to remain at -1 and therefore runtime PM
helpers return -EACCES.

Thierry

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