Re: [PATCH 3/4] backlight: lm3630a: Use backlight_get_brightness helper in update_status

[Luca Weiss <luca@z3ntu.xyz>]

On Dienstag, 20. Februar 2024 15:11:07 CET Daniel Thompson wrote:
> On Tue, Feb 20, 2024 at 12:11:21AM +0100, Luca Weiss wrote:
> > As per documentation "drivers are expected to use this function in their
> > update_status() operation to get the brightness value.".
> >
> > With this we can also drop the manual backlight_is_blank() handling
> > since backlight_get_brightness() is already handling this correctly.
> >
> > Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
> 
> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
> 
> However...
> 
> > ---
> >  	/* disable sleep */
> > @@ -201,9 +202,9 @@ static int lm3630a_bank_a_update_status(struct backlight_device *bl)
> >  		goto out_i2c_err;
> >  	usleep_range(1000, 2000);
> >  	/* minimum brightness is 0x04 */
> > -	ret = lm3630a_write(pchip, REG_BRT_A, bl->props.brightness);
> > +	ret = lm3630a_write(pchip, REG_BRT_A, brightness);
> 
> ... then handling of the minimum brightness looks weird in this driver.
> 
> The range of the backlight is 0..max_brightness. Sadly the drivers
> are inconsistant regarding whether zero means off or just minimum,
> however three certainly isn't supposed to mean off! In other words the
> offsetting should be handled by driver rather than hoping userspace has
> some magic LM3630A mode.

I could also try and fix that..

1. Treat 1..4 as 4, so have backlight on at that minimum level? Probably
wouldn't be noticable that brightness 1=2=3=4. And the backlight will be
on compared to off as it is now.

2. Decrease max_brightness by 4 values, so probably 0..251 and shift the
values up in the driver so we get 4..255?

Or would you have some other idea here?

Regards
Luca

> 
> You didn't introduce this so this patch still has my R-b ...
> 
> 
> Daniel.
>