Re: [RFC PATCH 0/3] Initial plumbing for implementing DRM connector APIs in Rust

[Rahul Rameshbabu <sergeantsagara@protonmail.com>]

On Tue, 19 Aug, 2025 11:06:40 +0200 "Maxime Ripard" <mripard@kernel.org> wrote:
> Hi Rahul,
>
> On Mon, Aug 18, 2025 at 05:04:15AM +0000, Rahul Rameshbabu wrote:
>> I am working on a drm_connector scoped backlight API in Rust. I have been
>> looking through Hans de Goede's previous efforts on this topic to help
>> guide my design. My hope is to enable backlight control over external
>> displays through DDC or USB Monitor Control Class while also supporting
>> internal panels. In parallel, I would like to improve the driver
>> probing/selection mechanism when there are different candidates for driving
>> a backlight device. This initial RFC is mainly intended to sanity check
>> that the plumbing I have chosen for extending the DRM connector
>> functionality in Rust seems reasonable.
>
> It's a great goal, and I had that same discussion with Hans recently
> too, but I can't find the link between backling/DDC CI, and Rust. Can
> you elaborate?

Hi Maxime,

Sure, let me elaborate on this. You are right that plumbing DDC
CI/backlight support at the DRM connector level does not need to be
implemented in Rust.

If we look at Hans's proposal, the suggested phase 2 was to add a
drm_connector helper function for plumbing a pointer to the backlight
device implementation. I had some model differences with regards to how
the API would look like, mostly stemming from concerns about providing
better runtime overriding of the acpi_video_get_backlight_type based
backlight selection. However, I am aligned with the direction of scoping
at the drm_connector level. I basically was interested in implementing
this helper functionality in Rust instead of C, which is where Rust came
into play.

I was also interested in declaring and attaching a drm_property in Rust
for controlling properties such as backlight rather than updating the
drm_connector declaration in C as an experiment.

Let me know if you feel like this work would be better off as a C
implementation. I can also send out a detailed architecture proposal to
the mailing list if that would help.

Link: https://lore.freedesktop.org/wayland-devel/0d188965-d809-81b5-74ce-7d30c49fee2d@redhat.com/

Thanks,
Rahul Rameshbabu

>
> Maxime