Weird default vblank value in ov5693

[Hans de Goede <hdegoede@redhat.com>]

Hi All,

While adding vblank ctrl support to the ov2680 driver I was looking
at the vblank ctrl code in the ov5693 and I noticed something
which I believe is weird / undesirable.

When setting a new mode the ov5693 driver does not keep the current
vts value (adjusting vblank to keep vts and thus the framerare and
exposure unchanged).

Instead it calculates a new vts value, resetting the framerate
to 30 fps; or 60 fps for smaller resolutions and then sets
vblank to the new (vts - new_mode->height) and adjusts
the exposure control-range to fit within the new vts, potentially
also changing the exposure value.

This behavior of the ov5693 code means that switching resolution
also changes the framerate and the exposure value which seems
undesirable.

The vblank and hblank control values changes on setting a mode
is unavoidable but the framerate and exposure value changing
at the same time seems undesirable.

Note that this also halves the max supported exposure value
when going to a lower-res mode even when userspace never
touches the vblank control.

Regards,

Hans