linux-kernel - Re: [PATCH] GPU: DRM: VC4/V3D Replace wait

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Date:   Wed, 19 Feb 2020 14:51:37 -0800
From:   Eric Anholt <eric@...olt.net>
To:     James Hughes <james.hughes@...pberrypi.com>
Cc:     David Airlie <airlied@...ux.ie>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] GPU: DRM: VC4/V3D Replace wait_for macros in to remove
 use of msleep

On Mon, Feb 17, 2020 at 7:41 AM James Hughes
<james.hughes@...pberrypi.com> wrote:
>
> The wait_for macro's for Broadcom VC4 and V3D drivers used msleep
> which is inappropriate due to its inaccuracy at low values (minimum
> wait time is about 30ms on the Raspberry Pi).
>
> This patch replaces the macro with the one from the Intel i915 version
> which uses usleep_range to provide more accurate waits.
>
> Signed-off-by: James Hughes <james.hughes@...pberrypi.com>

To apply this, we're going to want to split the patch up between v3d
(with a fixes tag to the introduction of the driver, since it's a
pretty critical fix) and vc4 (where it's used in KMS, and we're pretty
sure we want it but changing timing like this in KMS paths is risky so
we don't want to backport to stable).  And adjust the commit messages
to have consistent prefixes to the rest of the commits to those
drivers.

I've been fighting with the drm maintainer tools today to try to apply
the patch, with no luck.   I'll keep trying, and if I succeed, I'll
push it.