Re: [PATCH] [media] davinci: vpfe: Add documentation

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

On Saturday 01 September 2012 12:57:07 Sakari Ailus wrote:
> On Wed, Aug 29, 2012 at 08:11:50PM +0530, Prabhakar Lad wrote:

[snip]

> > For test pattern you meant control to enable/disable it ?
> 
> There are two approaches I can think of.
> 
> One is a menu control which can be used to choose the test pattern (or
> disable it). The control could be standardised but the menu items would have
> to be hardware-specific since the test patterns themselves are not
> standardised.

Agreed. The test patterns themselves are highly hardware-specific.

>From personal experience with sensors, most devices implement a small, fixed 
set of test patterns that can be exposed through a menu control. However, some 
devices also implement more "configurable" test patterns. For instance the 
MT9V032 can generate horizontal, vertical or diagonal test patterns, or a 
uniform grey test pattern with a user-configurable value. This would then 
require two controls.

> The alternative is to have a boolean control to enable (and disable) the
> test pattern and then a menu control to choose which one to use. Using or
> implemeting the control to select the test pattern isn't even strictly
> necessary to get a test pattern out of the device: one can enable it without
> knowing which one it is.
> 
> So which one would be better? Similar cases include V4L2_CID_SCENE_MODE
> which is used to choose the scene mode from a list of alternatives. The main
> difference to this case is that the menu items of the scene mode control
> are standardised, too.
> 
> I'd be inclined to have a single menu control, even if the other menu items
> will be device-specific. The first value (0) still has to be documented to
> mean the test pattern is disabled.
> 
> Laurent, Hans: what do you think?

A menu control with value 0 meaning test pattern disabled has my preference as 
well.

-- 
Regards,

Laurent Pinchart