linux-kernel - Re: [PATCH v14 7/7] riscv: dts: thead: Add PWM fan and thermal control

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Message-ID: <3aa6f79e-2ebf-4aff-a23c-7e79929a85f9@samsung.com>
Date: Sat, 23 Aug 2025 12:13:47 +0200
From: Michal Wilczynski <m.wilczynski@...sung.com>
To: Drew Fustini <fustini@...nel.org>
Cc: Uwe Kleine-König <ukleinek@...nel.org>, Miguel Ojeda
	<ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng
	<boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas
	Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, Trevor
	Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, 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>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer
	Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Alexandre
	Ghiti <alex@...ti.fr>, Marek Szyprowski <m.szyprowski@...sung.com>, Benno
	Lossin <lossin@...nel.org>, Michael Turquette <mturquette@...libre.com>,
	Daniel Almeida <daniel.almeida@...labora.com>, linux-kernel@...r.kernel.org,
	linux-pwm@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v14 7/7] riscv: dts: thead: Add PWM fan and thermal
 control



On 8/22/25 22:49, Drew Fustini wrote:
> On Wed, Aug 20, 2025 at 10:35:42AM +0200, Michal Wilczynski wrote:
>> Add Device Tree nodes to enable a PWM controlled fan and it's associated
>> thermal management for the Lichee Pi 4A board.
>>
>> This enables temperature-controlled active cooling for the Lichee Pi 4A
>> board based on SoC temperature.
>>
>> Reviewed-by: Drew Fustini <fustini@...nel.org>
>> Tested-by: Drew Fustini <fustini@...nel.org>
>> Signed-off-by: Michal Wilczynski <m.wilczynski@...sung.com>
>> ---
>>  arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts | 67 +++++++++++++++++++++++
>>  1 file changed, 67 insertions(+)
> 
> Do you think it makes sense to coordinate this with the "Initial thermal
> management for Lichee Pi 4A board" series [1] from Icenowy?

Hi,
It seems to me like using the HW PWM is just a better solution for
driving the fans. However as pointed in the discussion currently Rust
requires LLVM, so people compiling with gcc will not be able to compile
the driver for some time until the gcc support becomes better.

I think there is a way to express in Device Tree the fallback logic -
if Rust not available then use SW PWM. So I guess the pragmatic way to
go is to merge SW PWM temporary fix first, and later when gcc becomes
better at compiling Rust patch it up to use HW PWM instead.

> 
> Thanks,
> Drew
> 
> [1] https://lore.kernel.org/linux-riscv/20250816093209.2600355-1-uwu@icenowy.me/
> 

Best regards,
-- 
Michal Wilczynski <m.wilczynski@...sung.com>