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Re: [PATCH v3 09/14] media: platform: pxa_camera: add buffer sequencing

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  Re: [PATCH v3 09/14] media: platform: pxa_camera: add buffer sequencing Robert Jarzmik <robert.jarzmik@free.fr> - 2016-08-15 15:30 +0200
    Re: [PATCH v3 09/14] media: platform: pxa_camera: add buffer  sequencing Hans Verkuil <hverkuil@xs4all.nl> - 2016-08-15 15:40 +0200
      Re: [PATCH v3 09/14] media: platform: pxa_camera: add buffer sequencing Robert Jarzmik <robert.jarzmik@free.fr> - 2016-08-15 16:50 +0200

#1462779 — Re: [PATCH v3 09/14] media: platform: pxa_camera: add buffer sequencing

Robert Jarzmik <robert.jarzmik@free.fr> writes:

> Add sequence numbers to completed buffers.
>
> Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
> ---
>  drivers/media/platform/soc_camera/pxa_camera.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/media/platform/soc_camera/pxa_camera.c b/drivers/media/platform/soc_camera/pxa_camera.c
> index d66443ac1f4d..8a65f126d091 100644
> --- a/drivers/media/platform/soc_camera/pxa_camera.c
> +++ b/drivers/media/platform/soc_camera/pxa_camera.c
> @@ -401,6 +402,7 @@ static void pxa_camera_start_capture(struct pxa_camera_dev *pcdev)
>  	unsigned long cicr0;
>  
>  	dev_dbg(pcdev_to_dev(pcdev), "%s\n", __func__);
> +	pcdev->buf_sequence = 0;

I'm not so sure this is the right place to reset the buffer sequence.

I've seen no documentation on the rules applicable to this sequence number:
 - should it be reset if a "start streaming" operation occurs ?
 - should it be reset if a streams stops by lack of video buffers queued ?
 - should it be reset in queue_setup() like in other drivers ?

Or should it _never_ be reset and only be a monotonic raising number ?

Cheers.

--
Robert

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#1462784 — Re: [PATCH v3 09/14] media: platform: pxa_camera: add buffer sequencing

On 08/15/2016 03:26 PM, Robert Jarzmik wrote:
> Robert Jarzmik <robert.jarzmik@free.fr> writes:
> 
>> Add sequence numbers to completed buffers.
>>
>> Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
>> ---
>>  drivers/media/platform/soc_camera/pxa_camera.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/media/platform/soc_camera/pxa_camera.c b/drivers/media/platform/soc_camera/pxa_camera.c
>> index d66443ac1f4d..8a65f126d091 100644
>> --- a/drivers/media/platform/soc_camera/pxa_camera.c
>> +++ b/drivers/media/platform/soc_camera/pxa_camera.c
>> @@ -401,6 +402,7 @@ static void pxa_camera_start_capture(struct pxa_camera_dev *pcdev)
>>  	unsigned long cicr0;
>>  
>>  	dev_dbg(pcdev_to_dev(pcdev), "%s\n", __func__);
>> +	pcdev->buf_sequence = 0;
> 
> I'm not so sure this is the right place to reset the buffer sequence.
> 
> I've seen no documentation on the rules applicable to this sequence number:
>  - should it be reset if a "start streaming" operation occurs ?

start_streaming is the recommended place for setting the counter to 0. It's what
v4l2-compliance expects.

It is not documented since 1) not every driver does this and 2) there may
be cases where this behavior is not desired.

That said, I have yet to see a driver where zeroing this in start_streaming
is not appropriate.

Regards,

	Hans

>  - should it be reset if a streams stops by lack of video buffers queued ?
>  - should it be reset in queue_setup() like in other drivers ?
> 
> Or should it _never_ be reset and only be a monotonic raising number ?
> 
> Cheers.
> 
> --
> Robert
> 

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#1462842

Hans Verkuil <hverkuil@xs4all.nl> writes:

> On 08/15/2016 03:26 PM, Robert Jarzmik wrote:
>> Robert Jarzmik <robert.jarzmik@free.fr> writes:
>> I've seen no documentation on the rules applicable to this sequence number:
>>  - should it be reset if a "start streaming" operation occurs ?
>
> start_streaming is the recommended place for setting the counter to 0. It's what
> v4l2-compliance expects.
>
> It is not documented since 1) not every driver does this and 2) there may
> be cases where this behavior is not desired.
>
> That said, I have yet to see a driver where zeroing this in start_streaming
> is not appropriate.

Thanks for the information Hans, I'll modify this patch accordingly.

Cheers.

--
Robert

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