Re: [PATCH v5 0/3] Add "link bpc" DRM property

[Xaver Hugl]

Am Do., 19. März 2026 um 13:28 Uhr schrieb Nicolas Frattaroli
<nicolas.frattaroli@xxxxxxxxxxxxx>:
>
> This series adds a new "link bpc" DRM property. It reflects the display
> link's actual achieved output bits per component, considering any
> degradation of the bit depth done by drivers for bandwidth or other
> reasons. The property's value is updated during an atomic commit, which
> is also when it fires an uevent if it changed to let userspace know.

Hi,
I think it's a really good idea to have a property for knowing the
actual bpc of the link... however, I do have one big concern with this
API specifically: It only gives me this information after a modeset.

With this limitation, I can at most show the user which bpc was chosen
after the apply display settings and have the end user manually test
and figure things out, but I cannot show in the UI which bpc will be
chosen with some configuration before they apply it, and I cannot do
atomic tests to find a desired tradeoff automatically on the
compositor side.

As a side note, for future patches relevant for compositors, please cc
wayland-devel. It really shouldn't be up to chance whether or not
compositor developers that would later use the API find out about it
before it's merged, and keeping track of all of dri-devel is way too
much to ask from userspace developers.

- Xaver