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

From: Rob Herring <robh+dt@kernel.org>
To: Nicolas Boichat <drinkcat@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Devicetree List <devicetree@vger.kernel.org>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>,
	David Airlie <airlied@linux.ie>,
	lkml <linux-kernel@vger.kernel.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Steven Price <steven.price@arm.com>,
	Mark Brown <broonie@kernel.org>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>,
	Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
	Hsin-Yi Wang <hsinyi@chromium.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 4/7] drm/panfrost: Add support for a second regulator for the GPU
Date: Thu, 9 Jan 2020 10:56:29 -0600	[thread overview]
Message-ID: <CAL_JsqKvNBCVkiE4zKn0aXdrV4Ncx2bB6+KRpM+aPpMVzS4XbQ@mail.gmail.com> (raw)
In-Reply-To: <CANMq1KBo8ND+YDHaCw3yZZ0RUr69-NSUcVbqu38DuZvHUB-LFw@mail.gmail.com>

On Wed, Jan 8, 2020 at 4:52 PM Nicolas Boichat <drinkcat@chromium.org> wrote:
>
> On Wed, Jan 8, 2020 at 9:23 PM Mark Brown <broonie@kernel.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
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