Re: v4l: how to get blanking clock count?

[Sylwester Nawrocki <snjw23@gmail.com>]

Hi Sakari,

On 12/31/2011 12:35 PM, Sakari Ailus wrote:
> On Sat, Dec 31, 2011 at 02:57:31PM +0800, Scott Jiang wrote:
>> 2011/12/31 Sakari Ailus <sakari.ailus@iki.fi>:
>>> On Fri, Dec 30, 2011 at 03:20:43PM +0800, Scott Jiang wrote:
>>>> Our bridge driver needs to know line clock count including active
>>>> lines and blanking area.
>>>> I can compute active clock count according to pixel format, but how
>>>> can I get this in blanking area in current framework?
>>>
>>> Such information is not available currently over the V4L2 subdev interface.
>>> Please see this patchset:
>>>
>>> <URL:http://www.spinics.net/lists/linux-media/msg41765.html>
>>>
>>> Patches 7 and 8 are probably the most interesting for you. This is an RFC
>>> patchset so the final implementation could well still change.
>>>
>> Hi Sakari,
>>
>> Thanks for your reply. Your patch added VBLANK and HBLANK control, but
>> my case isn't a user control.
>> That is to say, you can't specify a blanking control value for sensor.
> 
> I the case of your bridge, that may not be possible, but that's the only one
> I've heard of so I think it's definitely a special case. In that case the
> sensor driver can't be allowed to change the blanking periods while
> streaming is ongoing.

I agree, it's just a matter of adding proper logic at the sensor driver.
However it might be a bit tricky, the bridge would have to validate blanking
values before actually enabling streaming.

> framesamples proposed by Sylwester for v4l2_mbus_framefmt could, and
> probably should, be exposed as a control with similar property.

Yeah, I'm going to try to add it to your proposed image source control
class.

>> And you added pixel clock rate in mbus format, I think if I add two
>> more parametres such as VBLANK lines and HBLANK clocks I can solve
>> this problem. In fact, active lines and blanking lines are essential
>> params to define an image.
> 
> Only the active lines and rows are, blanking period is just an idle period
> where no image data is transferred. It does not affect the resulting image
> in any way.

--
Regards,
Sylwester