linux-kernel - Re: [PATCH RFC 0/3] Initial work for Rust abstraction for HID device driver development

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Message-ID: <f6rizzlygznuebh22psrdkzfki7jfjzfaamuolobvpbgxoxjoi@gfu2eyzrm5wl>
Date: Thu, 13 Mar 2025 17:31:53 +0100
From: Benjamin Tissoires <bentiss@...nel.org>
To: Rahul Rameshbabu <sergeantsagara@...tonmail.com>
Cc: linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-input@...r.kernel.org, dri-devel@...ts.freedesktop.org, Jiri Kosina <jikos@...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>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH RFC 0/3] Initial work for Rust abstraction for HID device
 driver development

Hi,

[quick reply because I am completely under the water for the next 2
weeks]

On Mar 13 2025, Rahul Rameshbabu wrote:
> Hello,
> 
> I am a hobbyist developer who has been working on a project to create a new Rust
> HID device driver and the needed core abstractions for writing more HID device
> drivers in Rust. My goal is to support the USB Monitor Control Class needed for
> functionality such as backlight control for monitors like the Apple Studio
> Display and Apple Pro Display XDR. A new backlight API will be required to
> support multiple backlight instances and will be mapped per DRM connector. The
> current backlight API is designed around the assumption of only a single
> internal panel being present. I am currently working on making this new API for
> DRM in parallel to my work on the HID side of the stack for supporting these
> displays.

Thanks a lot for this work, though I wonder if your goal is not too big,
too far from the HID point of view. HID is simple, and there is only a
few bindings that you would need to be able to make "simple" HID
drivers.

My assumption would be to introduce the binding with a functional but
small driver (like one that just changes the report descriptor, or does
a sime raw event processing). Then we can look at integrating with the
DRM interface.

Though it's up to you to decide how you want to play ;)

> 
>   https://binary-eater.github.io/tags/usb-monitor-control/
> 
> Julius Zint had attempted to do so a year ago with a C HID driver but was gated
> by the lack of an appropriate backlight API for external displays. I asked him
> for permission to do the work need in Rust and plan to accredit him for the HID
> report handling for backlight in the USB Monitor Control Class standard.
> 
>   https://lore.kernel.org/lkml/f95da7ff-06dd-2c0e-d563-7e5ad61c3bcc@redhat.com/
> 
> I was hoping to get initial feedback on this work to make sure I am on the right
> path for making a Rust HID abstraction that would be acceptable upstream. The
> patches compile with WERROR being disabled. This is necessary since Rust treats
> missing documentation comments as warnings (which is a good thing). I also need
> to go in and add more SAFETY comments.

K, I'll give you my opinion in the patches as the HID co-maintainer. I
do have a very little rust experience, but this is my first in kernel,
so I hope the more experience rust people here will chime in as well.

Cheers,
Benjamin

> 
> Thanks,
> Rahul Rameshbabu
> 
> Rahul Rameshbabu (3):
>   rust: core abstractions for HID drivers
>   rust: hid: USB Monitor Control Class driver
>   rust: hid: demo the core abstractions for probe and remove
> 
>  drivers/hid/Kconfig                |  16 ++
>  drivers/hid/Makefile               |   1 +
>  drivers/hid/hid_monitor_control.rs |  42 +++++
>  rust/bindings/bindings_helper.h    |   1 +
>  rust/kernel/hid.rs                 | 245 +++++++++++++++++++++++++++++
>  rust/kernel/lib.rs                 |   2 +
>  6 files changed, 307 insertions(+)
>  create mode 100644 drivers/hid/hid_monitor_control.rs
>  create mode 100644 rust/kernel/hid.rs
> 
> -- 
> 2.47.2
> 
>