On Tue, Apr 26, 2022 at 03:38:25PM -0400, Alex Deucher wrote: > On Tue, Apr 26, 2022 at 4:35 AM Pekka Paalanen <ppaala...@gmail.com> wrote: > > > > Hi all, > > > > I'm working on setting HDR & WCG video modes in Weston, and I thought > > setting "max bpc" KMS property on the connector would be a good idea. > > I'm confused about how it works though. > > > > I did some digging in > > https://gitlab.freedesktop.org/wayland/weston/-/issues/612 > > > > Summary: > > > > - Apparently the property was originally added as a manual workaround > > for sink hardware behaving badly with high depth. A simple end user > > setting for "max bpc" would suffice for this use. > > > > - Drivers will sometimes automatically choose a lower bpc than the "max > > bpc" value, but never bigger. > > > > - amdgpu seems to (did?) default "max bpc" to 8, meaning that I > > definitely want to raise it. > > > > If I always slam "max bpc" to the highest supported value for that > > property, do I lose more than workarounds for bad sink hardware? > > > > Do I lose the ability to set video modes that take too much bandwidth > > at uncapped driver-selected bpc while capping the bpc lower would allow > > me to use those video modes? > > You wouldn't lose workarounds for amdgpu, you'd just lose potential > modes. The reason we added this feature in the first place was > because users bought new 4K monitors and the driver capped them at > 30Hz because we always defaulted to the highest supported bpc. We got > tons of bug reports about 4k@60 not being available and that was due > to the fact that the bpc was set to something greater than 8. I'm not > sure what the right answer is. It really depends on whether the user > wants higher bpc or faster refresh rates and possibly additional > higher res modes.
IMO the right answer is to do mode filtering based on the min bpc. -- Ville Syrjälä Intel
