linux-kernel - [PATCH v3 3/4] ARM: dts: imx6qdl-colibri: backlight pwm: Simplify inverted backlight

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Message-Id: <20220513102616.48040-4-max.oss.09@gmail.com>
Date:   Fri, 13 May 2022 12:26:14 +0200
From:   Max Krummenacher <max.oss.09@...il.com>
To:     max.krummenacher@...adex.com
Cc:     Fabio Estevam <festevam@...il.com>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 3/4] ARM: dts: imx6qdl-colibri: backlight pwm: Simplify inverted backlight

From: Max Krummenacher <max.krummenacher@...adex.com>

Set #pwm-cells to the default 3 to gain access to the parameter
which allows inverting the PWM signal. This is useful to specify
a backlight which has its highest brightness at 0.

With the change to use the PWM with inverted polarity the PWM signal
is inverted to how it was before this patch.
This changes the meaning of the values in the brightness-levels
property. I.e. the duty-cycle changes from x/255 to (255-x)/255.
Keeping the brightness-levels will then have a big brightness
jump from 0 to 127 duty cycle, the other 6 steps will then be
barely noticeable.

Change the brightness-levels to provide the same brightness-levels
as before.

Signed-off-by: Max Krummenacher <max.krummenacher@...adex.com>

---

Changes in v3:
- Add the reason why brightness-levels needs a change to commit
  comment as proposed by Fabio Estevam

Changes in v2:
- Split to two patches as proposed by Fabio Estevam

 arch/arm/boot/dts/imx6qdl-colibri.dtsi | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/boot/dts/imx6qdl-colibri.dtsi b/arch/arm/boot/dts/imx6qdl-colibri.dtsi
index f0908b530f86..d91fae92c90a 100644
--- a/arch/arm/boot/dts/imx6qdl-colibri.dtsi
+++ b/arch/arm/boot/dts/imx6qdl-colibri.dtsi
@@ -6,6 +6,7 @@
  */
 
 #include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/pwm/pwm.h>
 
 / {
 	model = "Toradex Colibri iMX6DL/S Module";
@@ -13,13 +14,13 @@
 
 	backlight: backlight {
 		compatible = "pwm-backlight";
-		brightness-levels = <0 127 191 223 239 247 251 255>;
-		default-brightness-level = <1>;
+		brightness-levels = <0 4 8 16 32 64 128 255>;
+		default-brightness-level = <6>;
 		enable-gpios = <&gpio3 26 GPIO_ACTIVE_HIGH>; /* Colibri BL_ON */
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_gpio_bl_on>;
 		power-supply = <&reg_module_3v3>;
-		pwms = <&pwm3 0 5000000>;
+		pwms = <&pwm3 0 5000000 PWM_POLARITY_INVERTED>;
 		status = "disabled";
 	};
 
@@ -620,7 +621,6 @@
 
 /* Colibri PWM<A> */
 &pwm3 {
-	#pwm-cells = <2>;
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_pwm3>;
 	status = "disabled";
-- 
2.20.1