2017-06-08 Shuah Khan <shuahkhan@xxxxxxxxx>: > 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); Without my changes it also fills it before __enqueue_in_driver() when start_streaming wasn't called yet. So I don't think it really matters. > > 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. I will send a v2 as soon as I can, but from Thursday next week until the 25th I'll be on vacation. Gustavo
