linux-kernel - Re: [PATCH v2 4/7] drm/panfrost: Add support for a second regulator for the GPU

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Date:   Thu, 9 Jan 2020 10:56:29 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     Mark Brown <broonie@...nel.org>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Steven Price <steven.price@....com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>
Subject: Re: [PATCH v2 4/7] drm/panfrost: Add support for a second regulator
 for the GPU

On Wed, Jan 8, 2020 at 4:52 PM Nicolas Boichat <drinkcat@...omium.org> wrote:
>
> On Wed, Jan 8, 2020 at 9:23 PM Mark Brown <broonie@...nel.org> wrote:
> >
> > On Wed, Jan 08, 2020 at 01:23:34PM +0800, Nicolas Boichat wrote:
> >
> > > Some GPUs, namely, the bifrost/g72 part on MT8183, have a second
> > > regulator for their SRAM, let's add support for that.
> >
> > > +     pfdev->regulator_sram = devm_regulator_get_optional(pfdev->dev, "sram");
> > > +     if (IS_ERR(pfdev->regulator_sram)) {
> >
> > This supply is required for the devices that need it so I'd therefore
> > expect the driver to request the supply non-optionally based on the
> > compatible string rather than just hoping that a missing regulator isn't
> > important.
>
> That'd be a bit awkward to match, though... Currently all bifrost
> share the same compatible "arm,mali-bifrost", and it'd seem
> weird/wrong to match "mediatek,mt8183-mali" in this driver? I have no
> idea if any other Mali implementation will require a second regulator,
> but with the MT8183 we do need it, see below.

The current number of supported bifrost platforms is 0. It's only a
matter of time until SoC specific compatibles need to be used in the
driver. This is why we require them.

It could very well be that all bifrost implementations need 2
supplies. On chip RAMs are very frequently a separate thing which are
synthesized differently from logic. At least within a specific IP
model, I somewhat doubt there's a variable number of supplies. It
could be possible to connect both to the same supply, but the correct
way to handle that is both -supply properties point to the same
regulator.

Rob