linux-kernel - Re: [PATCH] vb2: V4L2_BUF_FLAG

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Date:	Mon, 20 Jun 2016 12:17:24 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:	Pawel Osciak <pawel@...iak.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	linux-media <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Dimitrios Katsaros <patcherwork@...il.com>
Subject: Re: [PATCH] vb2: V4L2_BUF_FLAG_DONE is set after DQBUF

On 06/20/2016 12:12 PM, Ricardo Ribalda Delgado wrote:
> Good catch :)
> 
> I will prepare the new version. Btw, can I also merge
> vb2_internal_dqbuf and vb2_dqbuf in one function? Seems a bit
> overkilled that split.

No, that's not possible. vb2_internal_dqbuf is used in the threading
code to implement read() and vb2_fileio_is_active() returns true in that
case.

> 
> Regarding v42l_compliance... I can take care of that if you dare :)

It would be great if you can add a test for this.

Regards,

	Hans

> 
> Best regards!
> 
> On Mon, Jun 20, 2016 at 11:53 AM, Hans Verkuil <hverkuil@...all.nl> wrote:
>> On 06/20/2016 11:01 AM, Ricardo Ribalda Delgado wrote:
>>> According to the doc, V4L2_BUF_FLAG_DONE is cleared after DQBUF:
>>>
>>> V4L2_BUF_FLAG_DONE 0x00000004  ... After calling the VIDIOC_QBUF or
>>> VIDIOC_DQBUF it is always cleared ...
>>>
>>> Unfortunately, it seems that videobuf2 keeps it set after DQBUF. This
>>> can be tested with vivid and dev_debug:
>>>
>>> [257604.338082] video1: VIDIOC_DQBUF: 71:33:25.00260479 index=3,
>>> type=vid-cap, flags=0x00002004, field=none, sequence=163,
>>> memory=userptr, bytesused=460800, offset/userptr=0x344b000,
>>> length=460800
>>>
>>> This patch changes the order when fill_user_buffer() is called,
>>> to follow the documentation.
>>>
>>> Reported-by: Dimitrios Katsaros <patcherwork@...il.com>
>>> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
>>
>> Sorry, this won't work. Calling __vb2_dqbuf will overwrite the state
>> VB2_BUF_STATE_ERROR and so the V4L2_BUF_FLAG_ERROR flag will never be
>> set. The same is true for the last 'if' in the __fill_v4l2_buffer()
>> function.
>>
>> I think it might be better to keep this code and instead change the
>> vb2_internal_dqbuf function to just clear the DONE flag after calling
>> vb2_core_dqbuf.
>>
>> It would be nice to have a v4l2_compliance check for this as well.
>>
>> Regards,
>>
>>         Hans
>>
>>> ---
>>>  drivers/media/v4l2-core/videobuf2-core.c | 8 ++++----
>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
>>> index 633fc1ab1d7a..63981f28075e 100644
>>> --- a/drivers/media/v4l2-core/videobuf2-core.c
>>> +++ b/drivers/media/v4l2-core/videobuf2-core.c
>>> @@ -1771,10 +1771,6 @@ int vb2_core_dqbuf(struct vb2_queue *q, unsigned int *pindex, void *pb,
>>>       if (pindex)
>>>               *pindex = vb->index;
>>>
>>> -     /* Fill buffer information for the userspace */
>>> -     if (pb)
>>> -             call_void_bufop(q, fill_user_buffer, vb, pb);
>>> -
>>>       /* Remove from videobuf queue */
>>>       list_del(&vb->queued_entry);
>>>       q->queued_count--;
>>> @@ -1784,6 +1780,10 @@ int vb2_core_dqbuf(struct vb2_queue *q, unsigned int *pindex, void *pb,
>>>       /* go back to dequeued state */
>>>       __vb2_dqbuf(vb);
>>>
>>> +     /* Fill buffer information for the userspace */
>>> +     if (pb)
>>> +             call_void_bufop(q, fill_user_buffer, vb, pb);
>>> +
>>>       dprintk(1, "dqbuf of buffer %d, with state %d\n",
>>>                       vb->index, vb->state);
>>>
>>>
> 
> 
>