On Thu, 5 Jul 2018 at 11:21, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > When doing an atomic modeset with ALLOW_MODESET drivers are allowed to > pull in arbitrary other resources, including CRTCs (e.g. when > reconfiguring global resources). > > But in nonblocking mode userspace has then no idea this happened, > which can lead to spurious EBUSY calls, both: > - when that other CRTC is currently busy doing a page_flip the > ALLOW_MODESET commit can fail with an EBUSY > - on the other CRTC a normal atomic flip can fail with EBUSY because > of the additional commit inserted by the kernel without userspace's > knowledge > > For blocking commits this isn't a problem, because everyone else will > just block until all the CRTC are reconfigured. Only thing userspace > can notice is the dropped frames without any reason for why frames got > dropped. > > Consensus is that we need new uapi to handle this properly, but no one > has any idea what exactly the new uapi should look like. As a stop-gap > plug this problem by demoting nonblocking commits which might cause > issues by including CRTCs not in the original request to blocking > commits. Thanks for writing this up Daniel, and for reminding me about it some time later as well ... Reviewed-by: Daniel Stone <daniels@xxxxxxxxxxxxx> Cheers, Daniel
