linux-kernel - Re: [PATCH 3/4] backlight: lm3630a: Use backlight_get_brightness helper in update

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Date: Tue, 20 Feb 2024 14:11:07 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Luca Weiss <luca@...tu.xyz>
Cc: ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
	Lee Jones <lee@...nel.org>, Jingoo Han <jingoohan1@...il.com>,
	Helge Deller <deller@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"G.Shark Jeong" <gshark.jeong@...il.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Maximilian Weigand <mweigand@...igand.net>,
	dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 3/4] backlight: lm3630a: Use backlight_get_brightness
 helper in update_status

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@...tu.xyz>

Reviewed-by: Daniel Thompson <daniel.thompson@...aro.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.

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


Daniel.