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

On Tue, Feb 20, 2024 at 05:43:32PM +0100, Luca Weiss wrote:

On Dienstag, 20. Februar 2024 15:11:07 CET Daniel Thompson wrote:

quoted

On Tue, Feb 20, 2024 at 12:11:21AM +0100, Luca Weiss wrote:

quoted

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 <redacted>

Reviewed-by: Daniel Thompson <redacted>

However...

quoted

---
 	/* 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?

I think #2 is the right option but shouldn't it be decrease max_brightness
by 3, yielding 0..252 .

Only nitpicking on that because, given how old this driver is I'd like
to be conservative. I don't expect there to be userspaces with magic
LM3630A modes but there could be some that assume #0 is off! Hence I
wanted to make sure we are on the same page.


Daniel.