Re: [RFC] V4L2 API for flash devices

[Sakari Ailus <sakari.ailus@nokia.com>]

Sakari Ailus wrote:
> Hans Verkuil wrote:
>> On Tuesday, March 29, 2011 11:35:19 Sakari Ailus wrote:
>>> Hi Hans,
>>>
>>> Many thanks for the comments!
>>>
> 
> ...
> 
>>> It occurred to me that an application might want to turn off a flash
>>> which has been strobed on software. That can't be done on a single
>>> button control.
>>>
>>> V4L2_CID_FLASH_SHUTDOWN?
>>>
>>> The application would know the flash strobe is ongoing before it
>>> receives a timeout fault. I somehow feel that there should be a control
>>> telling that directly.
>>>
>>> What about using a bool control for the strobe?
>>
>> It depends: is the strobe signal just a pulse that kicks off the flash, or is 
>> it active throughout the flash duration? In the latter case a bool makes 
>> sense, in the first case an extra button control makes sense.
> 
> I like buttons since I associate them with action (like strobing) but on
> the other hand buttons don't allow querying the current state. On the
> other hand, the current state isn't always determinable, e.g. in the
> absence of the interrupt line from the flash controller interrupt pin
> (e.g. N900!).

Oh, I need to take my words back a bit.

There indeed is a way to get the on/off status for the flash, but that
involves I2C register access --- when you read the fault registers, you
do get the state, even if the interrupt linke is missing from the
device. At least I can't see why this wouldn't work, at least on this
particular chip.

What you can't have in this case is the event.

So, in my opinion this suggests that a single boolean control is the way
to go.

Regards,

-- 
Sakari Ailus
sakari.ailus@maxwell.research.nokia.com