Hi Rahul,

On Wed, Aug 20, 2025 at 04:46:52AM +0000, Rahul Rameshbabu wrote:

On Tue, 19 Aug, 2025 11:06:40 +0200 "Maxime Ripard" [off-list ref] wrote:

quoted

Hi Rahul,

On Mon, Aug 18, 2025 at 05:04:15AM +0000, Rahul Rameshbabu wrote:

quoted

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 for the explanation.

I'm not sure Rust is at the point where we can use it for the framework.
If we want to make this work useful, we have to make it consistent and
usable across all drivers, but we do have drivers for architectures that
aren't supported by Rust yet (let alone tier 1).

So it feels to me that it would be a bit premature for that work to be
in Rust. If you do want to use it from a Rust driver though, feel free
to write bindings for it, that would be a great addition.

Maxime