Re: [PATCH RFC 0/6] Rust Abstractions for PWM subsystem with TH1520 PWM driver

[Drew Fustini <pdp7pdp7@gmail.com>]

On Sat, May 24, 2025 at 11:14:54PM +0200, Michal Wilczynski wrote:
> This patch series introduces Rust support for the T-HEAD TH1520 PWM
> controller and demonstrates its use for fan control on the Sipeed Lichee
> Pi 4A board.
> 
> The primary goal of this patch series is to introduce a basic set of
> Rust abstractions for the Linux PWM subsystem. As a first user and
> practical demonstration of these abstractions, the series also provides
> a functional PWM driver for the T-HEAD TH1520 SoC. This allows control
> of its PWM channels and ultimately enables temperature controlled fan
> support for the Lichee Pi 4A board. This work aims to explore the use of
> Rust for PWM drivers and lay a foundation for potential future
> Rust based PWM drivers.
> 
> The series is structured as follows:
> 
> Patch 1/6: Introduce basic PWM abstractions
> This patch lays the groundwork by adding a Kconfig option for Rust PWM
> abstractions, necessary C helper functions, and a new Rust module
> (rust/kernel/pwm.rs). This module provides initial safe wrappers for
> core PWM data structures (Chip, Device, State, Args, Polarity) and
> functions (devm_chip_alloc, devm_chip_add), along with a basic PwmOps
> trait focusing on the .apply callback needed by PWM chip providers.
> 
> Patch 2/6: Add PWM driver for TH1520 SoC
> This introduces the Rust based PWM driver for the T-HEAD TH1520 SoC.
> It implements the PwmOps trait using the abstractions from the first
> patch and handles the specifics of the TH1520 hardware for configuring
> period, duty cycle, and polarity. Resource management leverages devm
> for the PWM chip and Rust DevRes for I/O memory, and RAII for clock
> handling.
> 
> Patch 3/6: dt-bindings: Add PWM T-HEAD controller dt-binding
> This patch adds the Device Tree binding documentation for the T-HEAD
> TH1520 PWM controller.
> 
> Patch 4/6: riscv: dts: thead:: Add PWM controller node
> This patch adds the actual Device Tree node for the TH1520 PWM controller.
> 
> Patch 5/6: riscv: dts: thead: Add PVT node
> Add pvt node for thermal sensor.
> 
> Patch 6/6: riscv: dts: thead: Add PWM fan and thermal control
> This final patch adds the Device Tree configuration for a PWM controlled
> fan to the Sipeed Lichee Pi 4A board DTS file. 
> 
> Testing:
> Tested on the TH1520 SoC. The fan works correctly.
> 
> Points for Discussion:
> The rust/kernel/pwm.rs abstraction layer is currently minimal,
> focusing on the immediate needs of this driver. Feedback on its design,
> scope, and potential for generalization would be highly appreciated.
> General feedback on the Rust implementation, FFI wrapping patterns, and
> adherence to kernel development practices is very welcome.
> 
> The patches are based on rust-next, with some dependencies which are not
> merged yet - platform Io support [1] and clk abstractions [2]. 
> 
> Reference repository with all the patches together can be found on
> github [3].
> 
> [1] - https://lore.kernel.org/rust-for-linux/20250509-topics-tyr-platform_iomem-v8-0-e9f1725a40da@collabora.com/
> [2] - https://lore.kernel.org/rust-for-linux/0ec0250c1170a8a6efb2db7a6cb49ae974d7ce05.1747634382.git.viresh.kumar@linaro.org/ 
> [3] - https://github.com/mwilczy/linux/commits/rust-next-pwm-working-fan-for-sending/

Thanks for the patch series. It will be great to have PWM working
upstream.

I've not built Linux with Rust before, so I'm going through the quick
start [1]. I've also never built Linux with LLVM before but clang seems
like the best compiler to use for Rust. Are you using LLVM?

Drew

[1] https://docs.kernel.org/rust/quick-start.html