On Fri, Aug 26, 2022 at 2:17 PM Simon Ser <contact@xxxxxxxxxxx> wrote: > > On Friday, August 26th, 2022 at 11:49, Sebastian Wick <sebastian.wick@xxxxxxxxxx> wrote: > > > > > +/* > > > > + * DRM_MODE_ATOMIC_ALLOW_MODESET > > > > + * > > > > + * Allow the update to result in visible artifacts such as a black screen. > > > > > > Maybe add: > > > > > > ...temporary or transient visible artifacts while the update is > > > being applied. Applying the update may also take significantly > > > more time than a page flip. The visual artifacts will not > > > appear after the update is completed. > > > > > > This flag must be set when the KMS update might cause visible > > > artifacts. Without this flag such KMS update will return EINVAL > > > error. What kind of updates may cause visible artifacts depends > > > on the driver and the hardware. Userspace that needs to know > > > beforehand if an update might cause visible artifacts can use > > > DRM_MODE_ATOMIC_TEST_ONLY without DRM_MODE_ATOMIC_ALLOW_MODESET > > > to see if it fails. > > > > > > Visual artifacts are guaranteed to not appear when this flag is > > > not set. > > > > That doesn't seem to be true, though. For example setting > > HDR_OUTPUT_METADATA for example does result in visual artifacts on my > > display no matter if the flag is specified or not because the > > artifacts are not the result of a mode set but of the display reacting > > to some AVI InfoFrame. > > One would need to read the HDMI spec to see if there's anything in > there about artifacts on AVI InfoFrame change, then figure out whether > this is a bug in the physical screen itself or whether the kernel > driver should require ALLOW_MODESET when updating the HDR metadata. I'm not even sure if that's the right thing to do. ALLOW_MODESET isn't really about if a commit can lead to visual artifacts but about keeping the existing links alive (someone with more knowledge on this subject probably has a better description for this). An async commit can also introduce visual artifacts for example and there are probably more cases. >
