linux-kernel - Re: [PATCH] venus: vdec: fix decoded data size

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Date:   Wed, 18 Jul 2018 17:37:55 +0300
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Nicolas Dufresne <nicolas@...fresne.ca>,
        Vikash Garodia <vgarodia@...eaurora.org>
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, acourbot@...omium.org
Subject: Re: [PATCH] venus: vdec: fix decoded data size

Hi,

On 07/18/2018 04:26 PM, Nicolas Dufresne wrote:
> Le mercredi 18 juillet 2018 à 14:31 +0300, Stanimir Varbanov a écrit :
>> Hi Vikash,
>>
>> On 07/02/2018 10:44 AM, Vikash Garodia wrote:
>>> Exisiting code returns the max of the decoded
>>> size and buffer size. It turns out that buffer
>>> size is always greater due to hardware alignment
>>> requirement. As a result, payload size given to
>>> client is incorrect. This change ensures that
>>> the bytesused is assigned to actual payload size.
>>>
>>> Change-Id: Ie6f3429c0cb23f682544748d181fa4fa63ca2e28
>>> Signed-off-by: Vikash Garodia <vgarodia@...eaurora.org>
>>> ---
>>>  drivers/media/platform/qcom/venus/vdec.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/media/platform/qcom/venus/vdec.c
>>> b/drivers/media/platform/qcom/venus/vdec.c
>>> index d079aeb..ada1d2f 100644
>>> --- a/drivers/media/platform/qcom/venus/vdec.c
>>> +++ b/drivers/media/platform/qcom/venus/vdec.c
>>> @@ -890,7 +890,7 @@ static void vdec_buf_done(struct venus_inst
>>> *inst, unsigned int buf_type,
>>>  
>>>  		vb = &vbuf->vb2_buf;
>>>  		vb->planes[0].bytesused =
>>> -			max_t(unsigned int, opb_sz, bytesused);
>>> +			min_t(unsigned int, opb_sz, bytesused);
>>
>> Most probably my intension was to avoid bytesused == 0, but that is
>> allowed from v4l2 driver -> userspace direction
> 
> It remains bad practice since it was used by decoders to indicate the
> last buffer. Some userspace (some GStreamer versions) will stop working
> if you start returning 0.

I think it is legal v4l2 driver to return bytesused = 0 when userspace
issues streamoff on both queues before EOS, no? Simply because the
capture buffers are empty.

-- 
regards,
Stan