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Subject: Re: [PATCH] venus: vdec: fix decoded data size
To:     Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        Nicolas Dufresne <nicolas@ndufresne.ca>,
        Vikash Garodia <vgarodia@codeaurora.org>
Cc:     linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, acourbot@chromium.org
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From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <33e8d8e3-138e-0031-5b75-4bef114ac75e@xs4all.nl>
Date:   Mon, 17 Sep 2018 12:00:34 +0200
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On 07/18/2018 04:37 PM, Stanimir Varbanov wrote:
> 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@codeaurora.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.
> 

Going through some of the older pending patches I found this one:

So is this patch right or wrong?

It's not clear to me.

Regards,

	Hans