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

[Michel Dänzer]

On 3/19/26 13:28, Nicolas Frattaroli wrote:
> 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.
> 
> There's a weston implementation at [1] which makes use of this new
> property to warn when a user's requested bpc could not be reached.
> 
> [1]: https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/1850

I see no description of a real-world use case, either in this series or in the weston MR, beyond logging a message when the "link bpc" & "max bpc" property values don't match. They are not expected to match in general, so I have a hard time seeing the usefulness of that.

Moreover, there's no description of what exactly the "link bpc" property value means, e.g. vs things like DSC or dithering, or how a compositor / user would determine which value they need / want under given circumstances.

In summary, I'm skeptical that this will be useful in practice in the current form. I do see potential for spurious bug reports based on the "link bpc" property having the "wrong" value though.


-- 
Earthling Michel Dänzer       \        GNOME / Xwayland / Mesa developer
https://redhat.com             \               Libre software enthusiast