On Wed, Apr 01, 2026 at 01:57:08PM +0200, Xaver Hugl wrote: > Am Do., 19. März 2026 um 13:28 Uhr schrieb Nicolas Frattaroli > <[email protected]>: > > > > 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.
I think the idea of some kind of feedback properties in the atomic commit has come up before, but no one has ever tried to implement them. > > 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 -- Ville Syrjälä Intel
