On 06/09/2017 12:25 AM, Gustavo Padovan wrote: > 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. Right, with this change, it fills the buffer before __enqueue_in_driver() when start_streaming is called. Is that an issue, I don't know for sure. It might not be necessary perhaps if buffer is filled in the path when stream is already called. > >> >> 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. okay sounds good. thanks, -- Shuah
