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

[Nicolas THERY <nicolas.thery@st.com>]

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As SUBDEV_S_CROP is obsolete, I wonder whether it is okay to support cropping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?

Thanks in advance.

Best regards,
Nicolas