linux-kernel - Re: [PATCH v10 0/7] Rust Abstractions for PWM subsystem with TH1520 PWM driver

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Message-ID: <8acb5b54-c01b-4427-9ada-596897b96a10@samsung.com>
Date: Fri, 11 Jul 2025 17:19:20 +0200
From: Michal Wilczynski <m.wilczynski@...sung.com>
To: Uwe Kleine-König <ukleinek@...nel.org>
Cc: 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>,
	Drew Fustini <fustini@...nel.org>, 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, Krzysztof
	Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v10 0/7] Rust Abstractions for PWM subsystem with TH1520
 PWM driver



On 7/10/25 22:39, Uwe Kleine-König wrote:
> Hello,
> 
> On Thu, Jul 10, 2025 at 06:58:41PM +0200, Michal Wilczynski wrote:
>> On 7/10/25 17:25, Uwe Kleine-König wrote:
>>> On Thu, Jul 10, 2025 at 03:48:08PM +0200, Michal Wilczynski wrote:
>>>> On 7/10/25 15:10, Uwe Kleine-König wrote:
>>>>> On Thu, Jul 10, 2025 at 10:42:07AM +0200, Michal Wilczynski wrote:
>>>>>> On 7/7/25 11:48, Michal Wilczynski wrote:
>>>>>>> The series is structured as follows:
>>>>>>>  - Expose static function pwmchip_release.
>>>>>
>>>>> Is this really necessary? I didn't try to understand the requirements
>>>>> yet, but I wonder about that. If you get the pwmchip from
>>>>> __pwmchip_add() the right thing to do to release it is to call
>>>>> pwmchip_remove(). Feels like a layer violation.
>>>>
>>>> It's required to prevent a memory leak in a specific, critical failure
>>>> scenario. The sequence of events is as follows:
>>>>
>>>>     pwm::Chip::new() succeeds, allocating both the C struct pwm_chip and
>>>>     the Rust drvdata.
>>>>
>>>>     pwm::Registration::register() (which calls pwmchip_add()) fails for
>>>>     some reason.
>>>
>>> If you called pwmchip_alloc() but not yet pwmchip_add(), the right
>>> function to call for cleanup is pwmchip_put().
>>>
>>>>     The ARef<Chip> returned by new() is dropped, its reference count
>>>>     goes to zero, and our custom release_callback is called.
>>>>
>>>> [...]
>>>>>>> ---
>>>>>>> base-commit: 47753b5a1696283930a78aae79b29371f96f5bca
>>>>>
>>>>> I have problems applying this series and don't have this base commit in
>>>>> my repo.
>>>>
>>>> Sorry for the confusion. Base commit doesn't exist in the mainline
>>>> kernel or linux-next, cause I've added some dependecies for compilation,
>>>> like IoMem for the driver (uploaded full branch on github [1]). The
>>>> bindings however doesn't depend on anything that's not in linux-next.
>>>
>>> The series didn't apply to my pwm/for-next branch.
>>>
>>> Note that the base-commit should always be a publically known commit.
>>> See the chapter about "Base Tree Information" in git-format-patch(1).
>>
>> Hello Uwe,
>>
>> Okay, thank you for the clarification. I understand the requirement for
>> a public base commit.
>>
>> My intention was to include the TH1520 driver primarily as a practical
>> demonstration of the new abstractions. However the driver can't be
>> merged as is, since it depends on the unmerged IoMem series and won't
>> compile against a public commit.
>>
>> I will rebase the series on pwm/for-next and drop the driver and its
>> associated device tree patches for now. I'll send a new version
>> containing just the core PWM abstraction patches, which apply cleanly.
>>
>> I will resubmit the driver patches once their dependencies are available
>> in a public tree.
> 
> If you base your tree on (say) v6.16-rc1, then add some Rust
> dependencies up to 47753b5a1696283930a78aae79b29371f96f5bca and then add
> your series, you just do:
> 
> 	git format-patch --base v6.16-rc1 47753b5a1696283930a78aae79b29371f96f5bca..
> 
> . This results in a base-commit line that I (and maybe also build bots)
> can use and a bunch of further lines listing the commits between
> v6.16-rc1 and 47753b5a1696283930a78aae79b29371f96f5bca that might be
> findable on lore.k.o.

Hi Uwe,

Thank you very much for the detailed advice on using git format-patch
--base. I appreciate you taking the time to explain the workflow.

I investigated this approach, and the difficulty is that the IoMem
series [1], which my driver depends on, is itself based on an
integration tree rather than a clean public tag.

This means that to create a series based on v6.16-rc1, I would have to
include a very large number of intermediate commits from linux-next,
which, would not be helpful for review.

Therefore, I believe that dropping the driver and its device tree
patches for now is the best path forward. This will result in a much
smaller, self contained series for the core PWM abstractions that
applies cleanly to your pwm/for-next branch.


[1] - https://lore.kernel.org/rust-for-linux/20250704-topics-tyr-platform_iomem-v12-0-1d3d4bd8207d@collabora.com/
> 
> Best regards
> Uwe

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