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? Or, are drivers required to choose a lower-than-usual but highest usable bpc to make the requested video mode squeeze through the connector and link? Do I need to implement a fallback strategy in a display server, starting from the highest possible "max bpc" value, and if my modeset is rejected, repeatedly try with lower "max bpc" setting until it works or I'm out of bpc options? Thanks, pq
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