linux-kernel - Re: [PATCH v3 6/8] riscv: dts: thead: Add GPU power sequencer node

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Message-ID: <CAMRc=Me75aGMic-GZuqCe+v=8MmmK8DCyfVZj=ELR4VuG-_qDQ@mail.gmail.com>
Date: Wed, 4 Jun 2025 14:33:00 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Drew Fustini <drew@...7.com>, Guo Ren <guoren@...nel.org>, 
	Fu Wei <wefu@...hat.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Philipp Zabel <p.zabel@...gutronix.de>, Frank Binns <frank.binns@...tec.com>, 
	Matt Coster <matt.coster@...tec.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 6/8] riscv: dts: thead: Add GPU power sequencer node

On Tue, Jun 3, 2025 at 8:45 PM Michal Wilczynski
<m.wilczynski@...sung.com> wrote:
>
>
>
> On 6/3/25 15:22, Krzysztof Kozlowski wrote:
> > On Fri, May 30, 2025 at 12:23:53AM GMT, Michal Wilczynski wrote:
> >> Add the device tree node for the T-HEAD TH1520 GPU power sequencer
> >> (gpu_pwrseq) to the th1520.dtsi file.
> >>
> >> This node instantiates the thead,th1520-gpu-pwrseq driver, which
> >
> > Explain the hardware, not what drivers do.
> >
> >> is responsible for managing the GPU's power-on/off sequence. The node
> >> specifies the gpu-clkgen reset, which is one of the resources
> >> controlled by this sequencer.
> >>
> >> Signed-off-by: Michal Wilczynski <m.wilczynski@...sung.com>
> >> ---
> >>  arch/riscv/boot/dts/thead/th1520.dtsi | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >> diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
> >> index bdbb1b985b0b76cf669a9bf40c6ec37258329056..6170eec79e919b606a2046ac8f52db07e47ef441 100644
> >> --- a/arch/riscv/boot/dts/thead/th1520.dtsi
> >> +++ b/arch/riscv/boot/dts/thead/th1520.dtsi
> >> @@ -238,6 +238,12 @@ aon: aon {
> >>              #power-domain-cells = <1>;
> >>      };
> >>
> >> +    gpu_pwrseq: pwrseq {
> >
> > Node names should be generic. See also an explanation and list of
> > examples (not exhaustive) in DT specification:
> > https://protect2.fireeye.com/v1/url?k=a53ea5d3-c4434f50-a53f2e9c-74fe48600158-c81092475ef416b3&q=1&e=d333d06b-0b06-493e-a358-e29ca542dfe7&u=https%3A%2F%2Fdevicetree-specification.readthedocs.io%2Fen%2Flatest%2Fchapter2-devicetree-basics.html%23generic-names-recommendation
> >
> >> +            compatible = "thead,th1520-gpu-pwrseq";
> >> +            resets = <&rst TH1520_RESET_ID_GPU_CLKGEN>;
> >> +            reset-names = "gpu-clkgen";
> >
> > What is the point of pwrseq if there is no consumer/user of it? Looks
> > like simple placeholder and anyway maybe the future consumer should just
> > use reset directly.
>
> Yeah I think you're right, I wanted to explore adding the pwrseq
> provider in separate node per discussion in v2 [1]. But for the v4 I
> think I'll revert to the v2 way of handling this reset [2].
>
> [1] - https://lore.kernel.org/all/CAPDyKFpi6_CD++a9sbGBvJCuBSQS6YcpNttkRQhQMTWy1yyrRg@mail.gmail.com/
> [2] - https://lore.kernel.org/all/20250414-apr_14_for_sending-v2-2-70c5af2af96c@samsung.com/
>

I think you still need to connect the GPU node with its pwrseq
provider (which will be the aon node in this case). But you already
have this link - the aon power domain. You can parse it in the pwrseq
match callback to determine which GPU is powered by which AON module.

Bart