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

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Message-ID: <8f63a814-1310-4edd-9394-38f71e017edb@samsung.com>
Date: Sat, 23 Aug 2025 12:17:27 +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 8/23/25 12:13, Michal Wilczynski wrote:
> 
> 
> 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 -

Sorry I meant 'there is NO way to express this in Device tree'

> 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,

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