Hi Gerd, On Mittwoch, 18. Dezember 2019 14:40:37 CET Gerd Hoffmann wrote: > Hi, > > > +The device MUST mark the last buffer with the > > +VIRTIO_VIDEO_BUFFER_F_EOS flag to denote completion of the drain > > +sequence. > > No, that would build a race condition into the protocol. The device > could complete the last buffer after the driver has sent the drain > command but before the device saw it. So the flag would not be > reliable. No, then it means the device was not in drain, but, for example, hit a resolution change in the stream and tells us that this is the last buffer with the old resolution. > > I also can't see why the flag is needed in the first place. The driver > should know which buffers are queued still and be able to figure > whenever the drain is complete or not without depending on that flag. > So I'd suggest to simply drop it. This flag is used not for drain only. In marks the completion of whatever specific buffer sequence, like a full end-of-stream, resolution change, drain etc. We also need this to handle nested sequences. For instance, a resolution change event might happen while in drain. Regards, Dmitry. > > That is the only issue I've spotted in the protocol on a first quick > look. There are a few places where the spec text could be improved. > I'll try to set aside some time to go over this in detail, but I can't > promise I'll find the time to do that before xmas and new year. > > cheers, > Gerd
