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Subject: Re: [PATCH] venus: vdec: fix decoded data size
To:     Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        Alexandre Courbot <acourbot@chromium.org>,
        Hans Verkuil <hverkuil@xs4all.nl>
Cc:     Nicolas Dufresne <nicolas@ndufresne.ca>, vgarodia@codeaurora.org,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        linux-arm-msm@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
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From:   Stanimir Varbanov <stanimir.varbanov@linaro.org>
Message-ID: <18c14931-15b4-190e-eb03-5cae8f8db381@linaro.org>
Date:   Tue, 2 Oct 2018 10:38:18 +0300
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Hi,

On 09/19/2018 06:02 PM, Stanimir Varbanov wrote:
> Hi Alex,
> 
> On 09/19/2018 01:32 PM, Alexandre Courbot wrote:
>> On Mon, Sep 17, 2018 at 11:33 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>>
>>> On 09/17/2018 04:30 PM, Stanimir Varbanov wrote:
>>>> Hi Hans,
>>>>
>>>> On 09/17/2018 01:00 PM, Hans Verkuil wrote:
>>>>> 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?
>>>>
>>>> I'm not sure either, let's not applying it for now (if Nicolas is right
>>>> this will break gstreamer plugin).
>>>>
>>>
>>> OK, I marked this as Rejected. If you change your mind it can be reposted :-)
>>
>> Mmm I'm not saying it has to be done in the current form, but at the
>> moment the returned bytesused seems to be wrong (at least Chrome is
>> not happy). We are returning the total size of the buffer instead of
>> the actually useful payload.
>>
>> If the intent is to avoid returning bytesused == 0 except for the
>> special case of the last buffer, how about the following?
>>
>> --- a/drivers/media/platform/qcom/venus/vdec.c
>> +++ b/drivers/media/platform/qcom/venus/vdec.c
>> @@ -943,8 +943,7 @@ static void vdec_buf_done(struct venus_inst *inst,
>> unsigned int buf_type,
>>                unsigned int opb_sz = venus_helper_get_opb_size(inst);
>>
>>                vb = &vbuf->vb2_buf;
>> -               vb->planes[0].bytesused =
>> -                       max_t(unsigned int, opb_sz, bytesused);
>> +                vb2_set_plane_payload(vb, 0, bytesused ? : opb_sz);
>>                vb->planes[0].data_offset = data_offset;
>>                vb->timestamp = timestamp_us * NSEC_PER_USEC;
>>                vbuf->sequence = inst->sequence_cap++;
>>
>> It works fine for me, and should not return 0 more often than it did
>> before (i.e. never). In practice I also never see the firmware
>> reporting a payload of zero on SDM845, but maybe older chips differ?
> 
> yes, it looks fine. Let me test it with older versions.
> 

OK, I played a bit with vb2_set_plane_payload(vb, 0, bytesused)

On v1 I see a buffer with LAST flag and bytesused == 0 (when
V4L2_DEC_CMD_STOP is used), after that after session_stop (first
streamoff) is called I see the rest of the capture buffers returned with
bytesused == 0.

So I think we can go ahead.

Vikash, can you resend with such a change?

-- 
regards,
Stan