Re: [RFC v2] V4L2 API for flash devices

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

Nayden Kanchev wrote:
> Hi Sakari,
> 
> Thanks for the update. I have just one comment about strobe types.

Hi Nayden,

Thanks for the comments!

> <snip>
> 
> 
> On 04/06/2011 11:10 AM, Sakari Ailus wrote:
>> - Added an open question on a new control:
>> V4L2_CID_FLASH_EXTERNAL_STROBE_WHENCE.
>>
>>
>>
> <snip>
>> 2. External strobe edge / level
>> -------------------------------
>>
>> No use is seen currently for this, but it may well appear, and the
>> hardware supports this. Level based trigger should be used since it is
>> more precise.
>>
>>     V4L2_CID_FLASH_EXTERNAL_STROBE_WHENCE
>>
>> Whether the flash controller considers external strobe as edge, when the
>> only limit of the strobe is the timeout on flash controller, or level,
>> when the flash strobe will last as long as the strobe signal, or as long
>> until the timeout expires.
>>
>> enum v4l2_flash_external_strobe_whence {
>>     V4L2_CID_FLASH_EXTERNAL_STROBE_LEVEL,
>>     V4L2_CID_FLASH_EXTERNAL_STROBE_EDGE,
>> };

Removed "CID_":

enum v4l2_flash_external_strobe_whence {
	V4L2_FLASH_EXTERNAL_STROBE_LEVEL,
	V4L2_FLASH_EXTERNAL_STROBE_EDGE,
};

I guess this should be an rw menu control for LED flash?

> 
> I agree that control over the strobe usage (level/edge) is required.
> Although we have some bad experience will lack of detailed information
> how exactly the flash chip will use those signals.
> 
> For example with AS3645A flash driver strobing by edge produced really
> strange flash output - light intensity was changing during the process
> and flash was stopped before the HW timeout.
> 
> On the other hand strobing by level didn't cause problems.
> 
> So even if HW supports some functionally we should prevent such
> malfunctioning by adding some restrictions in the board code also.

I agree.

The control should be probably exposed to tell which kind of
functionality does the flash chip provide, even if the menu has just one
option in it.

> I would also rename xxx_STROBE_WHENCE to xxx_STROBE_TYPE but it is just
> a suggestion :)

Sounds good to me.

V4L2_CID_FLASH_STROBE_MODE should be renamed to
V4L2_CID_FLASH_STROBE_WHENCE. That proper use of whence IMO. :-)

Regards,

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