linux-kernel - Re: [PATCH] drm/panfrost: Fix regulator_get

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Message-ID: <CAL_JsqKTJE=PURj_CJGXgR+=K=vn6YGfD4FJ6wuwNzvs=fOBQQ@mail.gmail.com>
Date:   Thu, 19 Sep 2019 11:55:08 -0500
From:   Rob Herring <robh@...nel.org>
To:     Steven Price <steven.price@....com>
Cc:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] drm/panfrost: Fix regulator_get_optional() misuse

On Mon, Sep 9, 2019 at 11:22 AM Steven Price <steven.price@....com> wrote:
>
> On 09/09/2019 16:41, Rob Herring wrote:
> > On Fri, Sep 6, 2019 at 4:23 PM Steven Price <steven.price@....com> wrote:
> >>
> >> On 04/09/2019 13:30, Mark Brown wrote:
> >>> The panfrost driver requests a supply using regulator_get_optional()
> >>> but both the name of the supply and the usage pattern suggest that it is
> >>> being used for the main power for the device and is not at all optional
> >>> for the device for function, there is no meaningful handling for absent
> >>> supplies.  Such regulators should use the vanilla regulator_get()
> >>> interface, it will ensure that even if a supply is not described in the
> >>> system integration one will be provided in software.
> >>>
> >>> Signed-off-by: Mark Brown <broonie@...nel.org>
> >>
> >> Tested-by: Steven Price <steven.price@....com>
> >>
> >> Looks like my approach to this was wrong - so we should also revert the
> >> changes I made previously.
> >>
> >> ----8<----
> >> From fe20f8abcde8444bb41a8f72fb35de943a27ec5c Mon Sep 17 00:00:00 2001
> >> From: Steven Price <steven.price@....com>
> >> Date: Fri, 6 Sep 2019 15:20:53 +0100
> >> Subject: [PATCH] drm/panfrost: Revert changes to cope with NULL regulator
> >>
> >> Handling a NULL return from devm_regulator_get_optional() doesn't seem
> >> like the correct way of handling this. Instead revert the changes in
> >> favour of switching to using devm_regulator_get() which will return a
> >> dummy regulator instead.
> >>
> >> Reverts commit 52282163dfa6 ("drm/panfrost: Add missing check for pfdev->regulator")
> >> Reverts commit e21dd290881b ("drm/panfrost: Enable devfreq to work without regulator")
> >
> > Does a straight revert of these 2 patches not work? If it does work,
> > can you do that and send to the list. I don't want my hand slapped
> > again reverting things.
>
> I wasn't sure what was best here - 52282163dfa6 is a bug fix, so
> reverting that followed by e21dd290881b would (re-)introduce a
> regression for that one commit (i.e. not completely bisectable).
> Reverting in the other order would work, but seems a little odd.
> Squashing the reverts seemed the neatest option - but it's not my hand
> at risk... :)
>
> Perhaps it would be best to simply apply Mark's change followed by
> something like the following. That way it's not actually a revert!
> It also avoids (re-)adding the now redundant check in
> panfrost_devfreq_init().
>
> Steve
>
> ---8<----
> From fb2956acdf46ca04095ef11363c136dc94a1ab18 Mon Sep 17 00:00:00 2001
> From: Steven Price <steven.price@....com>
> Date: Fri, 6 Sep 2019 15:20:53 +0100
> Subject: [PATCH] drm/panfrost: Remove NULL checks for regulator
>
> devm_regulator_get() is now used to populate pfdev->regulator which
> ensures that this cannot be NULL (a dummy regulator will be returned if
> necessary). So remove the checks in panfrost_devfreq_target().
>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)

Okay, I've gone this route and applied Mark's patch and this one.

Rob