On 06/06/2014 11:50 AM, Hans de Goede wrote:
> Hi,
>
> On 06/05/2014 02:23 PM, Laurent Pinchart wrote:
>> The V4L2 specification states that
>>
>> "When the application did not call VIDIOC_QBUF or VIDIOC_STREAMON yet
>> the poll() function succeeds, but sets the POLLERR flag in the revents
>> field."
>>
>> The vb2_poll() function sets POLLERR when the queued buffers list is
>> empty, regardless of whether this is caused by the stream not being
>> active yet, or by a transient buffer underrun.
>>
>> Bring the implementation in line with the specification by returning
>> POLLERR only when the queue is not streaming. Buffer underruns during
>> streaming are not treated specially anymore and just result in poll()
>> blocking until the next event.
>
> After your patch the implementation is still not inline with the spec,
> queuing buffers, then starting a thread doing the poll, then doing the
> streamon in the main thread will still cause the poll to return POLLERR,
> even though buffers are queued, which according to the spec should be enough
> for the poll to block.
>
> The correct check would be:
>
> if (list_empty(&q->queued_list) && !vb2_is_streaming(q))
> eturn res | POLLERR;
Good catch! I should have seen that :-(
v4l2-compliance should certainly be extended to test this as well.
Regards,
Hans
>
> Regards,
>
> Hans
>
>
>>
>> Signed-off-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
>> Acked-by: Hans Verkuil <hans.verk...@cisco.com>
>> ---
>> drivers/media/v4l2-core/videobuf2-core.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c
>> b/drivers/media/v4l2-core/videobuf2-core.c
>> index 349e659..fd428e0 100644
>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>> @@ -2533,9 +2533,9 @@ unsigned int vb2_poll(struct vb2_queue *q, struct file
>> *file, poll_table *wait)
>> }
>>
>> /*
>> - * There is nothing to wait for if no buffers have already been queued.
>> + * There is nothing to wait for if the queue isn't streaming.
>> */
>> - if (list_empty(&q->queued_list))
>> + if (!vb2_is_streaming(q))
>> return res | POLLERR;
>>
>> if (list_empty(&q->done_list))
>>
--
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