Em 13-09-2010 10:49, Andy Walls escreveu:
> On Mon, 2010-09-13 at 08:45 -0300, Mauro Carvalho Chehab wrote:
>> Em 13-09-2010 05:06, Hans Verkuil escreveu:
>>> On Monday, September 13, 2010 09:04:18 Laurent Pinchart wrote:
>>>> Hi Hans,
>>>>
>>>> On Thursday 09 September 2010 13:48:58 Hans de Goede wrote:
>>>>> On 09/09/2010 03:29 PM, Hans Verkuil wrote:
>>>>>>> On 09/09/2010 08:55 AM, Peter Korsgaard wrote:
>>>>>>>> "Hans" == Hans Verkuil<[email protected]> writes:
>>>>>>>>
>>>>>>>> I originally was in favor of controlling these through v4l as well, but
>>>>>>>> people made some good arguments against that. The main one being: why
>>>>>>>> would you want to show these as a control? What is the end user
>>>>>>>> supposed
>>>>>>>> to do with them? It makes little sense.
>>>>
>>>> Status LEDs reflect in glasses, making annoying color dots on webcam
>>>> pictures.
>>>> That's why Logitech allows to turn the status LED off on its webcams.
>>>
>>> That's a really good argument. I didn't think of that one.
>>
>> There's one difference between illuminators and leds and anything else that
>> we use
>> currently via CTRL interface: all other controls affects just an internal
>> hardware
>> capability that are not visible to the user, nor can cause any kind of
>> damage or
>> annoyance.
>>
>> On the other hand, a LED and an illuminator that an application may forget
>> to turn
>> off could be very annoying, and may eventually reduce the lifecycle or a
>> device (in
>> the case of non-LED illuminators, for example).
>
> Yes, I can appreciate that. On driver unload and suspend that should
> certainly be the case for illuminators.
>
> However, I don't think that's a good idea for final close on a file
> descriptor though. That's a departure from normal V4L2 behavior.
This doesn't seem to be a good reason. Keeping a LED after its usage is
annoying to
the user, can cause damage on devices (reduce lifetime) and can draw lots of
power
from the batteries (on battery-powered devices).
> For a USB connected device, turning off the illuminator after the fact
> is simple, if the user has no other recourse: unplug the device. :)
Try to unplug the flash led on your cell phone ;)
>> So, a special treatment seems to be required for both cases: if the
>> application that
>> changed the LED or illuminator to ON dies or closes, the LED/illuminator
>> should be
>> turned off by the driver.
>
> That will break cases like these:
>
> $ v4l2-ctl -d /dev/video0 -c illuminator_2=1
> $ (command to run app that doesn't present all controls, e.g. cheese)
True, but it may have an alternative syntax for it, like:
v4l2-ctl -d /dev/video0 -c illuminator_2=1 --run cheese [<args>]
This way, if cheese or v4l2-ctl abends, the illuminator will be turned off.
Of course, we'll likely need to have a flag visible on userspace, to say that
such
control resets to an "off" state when the application dies, to avoid someone to
use it
like:
v4l2-ctl -d /dev/video0 -c illuminator_2=1
Cheers,
Mauro
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