Re: [PATCH/RFC v3 5/5] media: Add registration helpers for V4L2 flash sub-devices

[Jacek Anaszewski]

Hi Sakari,

On 05/02/2014 01:06 PM, Sakari Ailus wrote:

> > > > [...]
> > > > > > +static inline enum led_brightness v4l2_flash_intensity_to_led_brightness(
> > > > > > +					struct led_ctrl *config,
> > > > > > +					u32 intensity)
> > > > >
> > > > > Fits on a single line.
> > > > >
> > > > > > +{
> > > > > > +	return intensity / config->step;
> > > > >
> > > > > Shouldn't you first decrement the minimum before the division?
> > > >
> > > > Brightness level 0 means that led is off. Let's consider following case:
> > > >
> > > > intensity - 15625
> > > > config->step - 15625
> > > > intensity / config->step = 1 (the lowest possible current level)
> > >
> > > In V4L2 controls the minimum is not off, and zero might not be a possible
> > > value since minimum isn't divisible by step.
> > >
> > > I wonder how to best take that into account.
> >
> > I've assumed that in MODE_TORCH a led is always on. Switching
> > the mode to MODE_FLASH or MODE_OFF turns the led off.
> > This way we avoid the problem with converting 0 uA value to
> > led_brightness, as available torch brightness levels start from
> > the minimum current level value and turning the led off is
> > accomplished on transition to MODE_OFF or MODE_FLASH, by
> > calling brightness_set op with led_brightness = 0.
>
> I'm not sure if we understood the issue the same way. My concern was that if
> the intensity isn't a multiple of step (but intensity - min is), the above
> formula won't return a valid result (unless I miss something).

Please note that v4l2_flash_intensity_to_led_brightness is called only
from s_ctrl callback, and thus it expects to get the intensity aligned
to the step value, so it will always be a multiple of step.
Is it possible that s_ctrl callback would be passed a non-aligned
control value?

Regards,
Jacek Anaszewski

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