Re: how to crop/scale in mono-subdev camera sensor driver?

[Sylwester Nawrocki <sylvester.nawrocki@gmail.com>]

Hi,

On 09/14/2012 05:00 PM, Nicolas THERY wrote:
> Hello,
> 
> I'm studying how to support cropping and scaling (binning, skipping, digital
> scaling if any) for different models for camera sensor drivers.  There seems to
> be (at least) two kinds of sensor drivers:
> 
> 1) The smiapp driver has 2 or 3 subdevs: pixel array ->  binning (->  scaling).
> It gives clients full control over the various ways of cropping and scaling
> thanks to the selection API.
> 
> 2) The mt9p031 driver (and maybe others) has a single subdev.  Clients use the
> obsolete SUBDEV_S_CROP ioctl for selecting a region of interest in the pixel
> array and SUBDEV_S_FMT for setting the source pad mbus size.  If the mbus size
> differs from the cropping rectangle size, scaling is enabled and the driver
> decides internally how to combine skipping and binning to achieve the requested
> scaling factors.
> 
> As SUBDEV_S_CROP is obsolete, I wonder whether it is okay to support cropping
> and scaling in a mono-subdev sensor driver by (a) setting the cropping
> rectangle with SUBDEV_S_SELECTION on the source pad, and (b) setting the
> scaling factors via the source pad mbus size as in the mt9p031 driver?

Cc: Sakari, Laurent

AFAICT in a single subdev with one pad configuration your steps as above 
are valid, i.e. crop rectangle can be set with 
VIDIOC_SUBDEV_S_SELECTION(V4L2_SEL_TGT_CROP) and the sensor's output 
resolution with VIDIOC_SUBDEV_S_FMT.

I guess documentation [1] wasn't clear enough about that ?

The subdev crop ioctls are deprecated in favour of the selection API, so
now VIDIOC_SUBDEV_G/S_SELECTION ioctls and corresponding subdev ops needs 
to be used anywhere you would have used SUBDEV_G/S_CROP before.

This reminds me there are still a few drivers that need to be converted
to use set/get_selection subdev pad level ops, rather than set/get_crop.

[1] http://linuxtv.org/downloads/v4l-dvb-apis/subdev.html

--

Regards,
Sylwester