On 10/18/19 9:50 AM, Maxime Jourdan wrote:
> On Wed, Oct 9, 2019 at 2:01 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>>
>> On 10/8/19 3:40 PM, Maxime Jourdan wrote:
>>> On 07/10/2019 18:39, Hans Verkuil wrote:
>>>> On 10/7/19 6:24 PM, Maxime Jourdan wrote:
>>>>> On 07/10/2019 17:12, Hans Verkuil wrote:
>>>>>> On 10/7/19 4:59 PM, Maxime Jourdan wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> This patch series aims to bring H.264 support as well as compliance update
>>>>>>> to the amlogic stateful video decoder driver.
>>>>>>>
>>>>>>> There is 1 issue that remains currently:
>>>>>>>
>>>>>>> - The following codepath had to be commented out from v4l2-compliance as
>>>>>>> it led to stalling:
>>>>>>>
>>>>>>> if (node->codec_mask & STATEFUL_DECODER) {
>>>>>>> struct v4l2_decoder_cmd cmd;
>>>>>>> buffer buf_cap(m2m_q);
>>>>>>>
>>>>>>> memset(&cmd, 0, sizeof(cmd));
>>>>>>> cmd.cmd = V4L2_DEC_CMD_STOP;
>>>>>>>
>>>>>>> /* No buffers are queued, call STREAMON, then STOP */
>>>>>>> fail_on_test(node->streamon(q.g_type()));
>>>>>>> fail_on_test(node->streamon(m2m_q.g_type()));
>>>>>>> fail_on_test(doioctl(node, VIDIOC_DECODER_CMD, &cmd));
>>>>>>>
>>>>>>> fail_on_test(buf_cap.querybuf(node, 0));
>>>>>>> fail_on_test(buf_cap.qbuf(node));
>>>>>>> fail_on_test(buf_cap.dqbuf(node));
>>>>>>> fail_on_test(!(buf_cap.g_flags() & V4L2_BUF_FLAG_LAST));
>>>>>>> for (unsigned p = 0; p < buf_cap.g_num_planes(); p++)
>>>>>>> fail_on_test(buf_cap.g_bytesused(p));
>>>>>>> fail_on_test(node->streamoff(q.g_type()));
>>>>>>> fail_on_test(node->streamoff(m2m_q.g_type()));
>>>>>>>
>>>>>>> /* Call STREAMON, queue one CAPTURE buffer, then STOP */
>>>>>>> fail_on_test(node->streamon(q.g_type()));
>>>>>>> fail_on_test(node->streamon(m2m_q.g_type()));
>>>>>>> fail_on_test(buf_cap.querybuf(node, 0));
>>>>>>> fail_on_test(buf_cap.qbuf(node));
>>>>>>> fail_on_test(doioctl(node, VIDIOC_DECODER_CMD, &cmd));
>>>>>>>
>>>>>>> fail_on_test(buf_cap.dqbuf(node));
>>>>>>> fail_on_test(!(buf_cap.g_flags() & V4L2_BUF_FLAG_LAST));
>>>>>>> for (unsigned p = 0; p < buf_cap.g_num_planes(); p++)
>>>>>>> fail_on_test(buf_cap.g_bytesused(p));
>>>>>>> fail_on_test(node->streamoff(q.g_type()));
>>>>>>> fail_on_test(node->streamoff(m2m_q.g_type()));
>>>>>>> }
>>>>>>>
>>>>>>> The reason for this is because the driver has a limitation where all
>>>>>>> capturebuffers must be queued to the driver before STREAMON is effective.
>>>>>>> The firmware needs to know in advance what all the buffers are before
>>>>>>> starting to decode.
>>>>>>> This limitation is enforced via q->min_buffers_needed.
>>>>>>> As such, in this compliance codepath, STREAMON is never actually called
>>>>>>> driver-side and there is a stall on fail_on_test(buf_cap.dqbuf(node));
>>>>>>
>>>>>> That's interesting. I will have to look more closely at this.
>>
>> This requires a helper function in videobuf2-v4l2.c.
>>
>> In vdec_decoder_cmd you would need code like this:
>>
>> if (!vb2_start_streaming_called(&capture_queue)) {
>> vb2_dequeue_empty_last_buf(&capture_queue);
>> return 0;
>> }
>>
>> The vb2_dequeue_empty_last_buf (function name can probably be improved upon!)
>> does nothing if no capture buffers were queued, otherwise it takes the first
>> buffer, sets the LAST flag and sets bytesused to 0 and marks it as DONE.
>>
>> The driver cannot do this directly, since the buffers were never queued to the
>> driver and are owned by vb2.
>>
>> This is something that needs to be done for any codec driver that sets
>> min_buffers_needed to a value > 1.
>>
>> The vb2 function would look something like this:
>>
>> void vb2_dqbuf_empty_last_buf(struct vb2_queue *q)
>> {
>> struct vb2_buffer *vb;
>> struct vb2_v4l2_buffer *vbuf;
>> unsigned int i;
>>
>> if (WARN_ON(q->is_output))
>> return;
>> if (list_empty(&q->queued_list))
>> return;
>> vb = list_first_entry(&q->queued_list, struct vb2_buffer, queued_entry);
>> list_del(&vb->queued_entry);
>> for (i = 0; i < vb->num_planes; i++)
>> vb2_set_plane_payload(vb, i, 0)
>> vbuf = to_vb2_v4l2_buffer(vb);
>> vbuf->flags |= V4L2_BUF_FLAG_LAST;
>> vb2_buffer_done(vb, VB2_BUF_STATE_DONE);
>> }
>> EXPORT_SYMBOL_GPL(vb2_dqbuf_empty_last_buf);
>>
>> Neither compiled, nor tested, and I think this should be in v4l2-mem2mem.c instead of
>> in videobuf2-v4l2.c since this is very m2m specific.
>>
>> So see this as a suggestion :-)
>>
>> Anyway, the key take-away from this is that userspace does not know if your driver
>> behaves the way it does, so STOP should still produce a sane expected result.
>>
>> Which in this is just a single empty capture buffer marked LAST.
>
> Thanks, this makes sense. It doesn't quite fit the current usage
> unfortunately as the test in v4l2-compliance goes like this:
>
> fail_on_test(doioctl(node, VIDIOC_DECODER_CMD, &cmd));
> fail_on_test(buf_cap.querybuf(node, 0));
> fail_on_test(buf_cap.qbuf(node));
> fail_on_test(buf_cap.dqbuf(node));
> fail_on_test(!(buf_cap.g_flags() & V4L2_BUF_FLAG_LAST));
>
> Since the buffer is queued after issuing the stop cmd, it is not
> possible to flag it as DONE in vdec_decoder_cmd.
>
> A solution would be to hijack vidioc_qbuf and flag the buffer if a
> stop has been issued previously and the capture queue is not
> streaming. Would that be okay ?
Actually, I am wondering if this shouldn't be integrated into
v4l2-mem2mem.c. The corner case where you need to use an empty
last buffer is really awkward for drivers. So perhaps this should
be integrated into v4l2-mem2mem.c where you can mark that the
next queued buffer shall be immediately returned as an empty buffer
with the LAST flag set.
Since v4l2-mem2mem already has its own vidioc_qbuf function it can
easily be added there, and I think that's a much better place than
having to touch vb2 itself.
Regards,
Hans
>
> Maxime
>
>>
>> Regards,
>>
>> Hans
