Hi Tomasz, On Saturday, 20 October 2018 13:24:20 EEST Tomasz Figa wrote: > On Thu, Oct 18, 2018 at 7:03 PM Tomasz Figa wrote: > > On Wed, Oct 17, 2018 at 10:34 PM Laurent Pinchart wrote: > >> Hi Tomasz, > >> > >> Thank you for the patch. > > > > Thanks for your comments! Please see my replies inline. > > > >> On Tuesday, 24 July 2018 17:06:20 EEST Tomasz Figa wrote: > > [snip] > > >>> +4. At this point, decoding is paused and the driver will accept, but > >>> not > >>> + process any newly queued ``OUTPUT`` buffers until the client > >>> issues > >>> + ``V4L2_DEC_CMD_START`` or restarts streaming on any queue. > >>> + > >>> +* Once the drain sequence is initiated, the client needs to drive it > >>> to > >>> + completion, as described by the above steps, unless it aborts the > >>> process > >>> + by issuing :c:func:`VIDIOC_STREAMOFF` on ``OUTPUT`` queue. The client > >>> + is not allowed to issue ``V4L2_DEC_CMD_START`` or > >>> ``V4L2_DEC_CMD_STOP`` > >>> + again while the drain sequence is in progress and they will fail with > >>> + -EBUSY error code if attempted. > >> > >> While this seems OK to me, I think drivers will need help to implement > >> all the corner cases correctly without race conditions. > > > > We went through the possible list of corner cases and concluded that > > there is no use in handling them, especially considering how much they > > would complicate both the userspace and the drivers. Not even > > mentioning some hardware, like s5p-mfc, which actually has a dedicated > > flush operation, that needs to complete before the decoder can switch > > back to normal mode. > > Actually I misread your comment. > > Agreed that the decoder commands are a bit tricky to implement > properly. That's one of the reasons I decided to make the return > -EBUSY while an existing drain is in progress. > > Do you have any particular simplification in mind that could avoid > some corner cases? Not really on the spec side. I think we'll have to implement helper functions for drivers to use if we want to ensure a consistent and bug-free behaviour. -- Regards, Laurent Pinchart
