Hi Gustavo, On Thu, Jun 8, 2017 at 2:17 PM, Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx> wrote: > Hi Gustavo, > > Em Wed, 24 May 2017 21:31:01 -0300 > Gustavo Padovan <gustavo@xxxxxxxxxxx> escreveu: > >> Hi all, >> >> I've been working on the v2 of this series, but I think I hit a blocker >> when trying to cover the case where the driver asks to requeue the >> buffer. It is related to the out-fence side. >> >> In the current implementation we return on QBUF an out-fence fd that is not >> tied to any buffer, because we don't know the queueing order until the >> buffer is queued to the driver. Then when the buffer is queued we use >> the BUF_QUEUED event to notify userspace of the index of the buffer, >> so now userspace knows the buffer associated to the out-fence fd >> received earlier. >> >> Userspace goes ahead and send a DRM Atomic Request to the kernel to >> display that buffer on the screen once the fence signals. If it is >> a nonblocking request the fence waiting is past the check phase, thus >> it isn't allowed to fail anymore. >> >> But now, what happens if the V4L2 driver calls buffer_done() asking >> to requeue the buffer. That means the operation failed and can't >> signal the fence, starving the DRM side. >> >> We need to fix that. The only way I can see is to guarantee ordering of >> buffers when out-fences are used. Ordering is something that HAL3 needs >> to so maybe there is more than one reason to do it like this. I'm not >> a V4L2 expert, so I don't know all the consequences of such a change. >> >> Any other ideas? >> >> The current patchset is at: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/padovan/linux.git/log/?h=v4l2-fences Do you plan to send the v2 out? I did a quick review and have a few comments. [media] vb2: split out queueing from vb_core_qbuf() It changes the sequence a bit. /* Fill buffer information for the userspace */ if (pb) call_void_bufop(q, fill_user_buffer, vb, pb); With the changes - user information is filled before __enqueue_in_driver(vb); Anyway, it might be a good idea to send the v2 out for review and we can review patches in detail. I am hoping to test your patch series on odroid-xu4 next week. Could you please add me to the thread as well as include me when you send v2 and subsequent versions. thanks, -- Shuah
