Re: Switching input during capture

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 29-10-2011 05:52, Laurent Pinchart escreveu:
> Hi Mauro,
> 
> On Saturday 29 October 2011 00:30:12 Mauro Carvalho Chehab wrote:
>> Em 28-10-2011 14:42, Laurent Pinchart escreveu:
>>> On Friday 28 October 2011 03:31:53 Gilles Gigan wrote:
>>>> Hi,
>>>> I would like to know what is the correct way to switch the current
>>>> video input during capture on a card with a single BT878 chip and 4
>>>> inputs
>>>> (http://store.bluecherry.net/products/PV%252d143-%252d-4-port-video-capt
>>>> ur e-card-%2830FPS%29-%252d-OEM.html). I tried doing it in two ways: -
>>>> using VIDIOC_S_INPUT to change the current input. While this works, the
>>>> next captured frame shows video from the old input in its top half and
>>>> video from the new input in the bottom half.
>>
>> This is is likely easy to fix. The driver has already a logic to prevent
>> changing the buffer while in the middle of a buffer filling. I suspect
>> that the BKL removal patches might have broken it somewhat, allowing
>> things like that. basically, it should be as simple as not allowing
>> changing the input at the top half.
> 
> This will work optimally only if the input analog signals are synchronized, 
> right ? If we switch to a new input right when the frame start, can the first 
> frame captured on the new input be corrupted ?

That's a good question. I'm not sure how those bttv cards solve it, but as
they're widely used on such configurations, I suspect that the hardware used
on those CCTV boards have some logic to keep them in sync.

> 
>> Please try the enclosed patch.
>>
>> Regards,
>> Mauro
>>
>> -
>>
>> bttv: Avoid switching the video input at the top half.
>>
>> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
>>
>> diff --git a/drivers/media/video/bt8xx/bttv-driver.c
>> b/drivers/media/video/bt8xx/bttv-driver.c index 3dd0660..6a3be6f 100644
>> --- a/drivers/media/video/bt8xx/bttv-driver.c
>> +++ b/drivers/media/video/bt8xx/bttv-driver.c
>> @@ -3978,7 +3978,7 @@ bttv_irq_switch_video(struct bttv *btv)
>>  	bttv_set_dma(btv, 0);
>>
>>  	/* switch input */
>> -	if (UNSET != btv->new_input) {
>> +	if (! btv->curr.top && UNSET != btv->new_input) {
>>  		video_mux(btv,btv->new_input);
>>  		btv->new_input = UNSET;
>>  	}
>