setting volatile v4l2-control

[Jacek Anaszewski <j.anaszewski@samsung.com>]

While testing the LED / flash API integration patches
I noticed that the v4l2-controls marked as volatile with
V4L2_CTRL_FLAG_VOLATILE flag behave differently than I would
expect.

Let's consider following use case:

There is a volatile V4L2_CID_FLASH_INTENSITY v4l2 control with
following constraints:

min: 1
max: 100
step: 1
def: 1

1. Set the V4L2_CID_FLASH_INTENSITY control to 100.
	- as a result s_ctrl op is called
2. Set flash_brightness LED sysfs attribute to 10.
3. Set the V4L2_CID_FLASH_INTENSITY control to 100.
	- s_ctrl op isn't called

This way we are unable to write a new value to the device, despite
that the related setting was changed from the LED subsystem level.

I would expect that if a control is marked volatile, then
the v4l2-control framework should by default call g_volatile_ctrl
op before set and not try to use the cached value.

Is there some vital reason for not doing this?

-- 
Best Regards,
Jacek Anaszewski