[PATCH] arm64: dts: qcom: Fix backlight control on Dell Inspiron 7441

[Avalon Vargas via B4 Relay]

From: Avalon Vargas <avalon.vargas.centeno@xxxxxxxxxxxxx>

The AUO B140QAX01.H panel on tested Dell Inspiron 14 Plus 7441 units
advertises PWM brightness control but not AUX brightness setting.
Without a backlight described in the device tree, the panel falls back
to the AUX helper, which registers a backlight with max_brightness=0.
Brightness adjustment is consequently unavailable.

Enable PMK8550 PWM channel 0, route it through GPIO5, and connect a PWM
backlight to the panel. Provide an interpolated brightness table with
101 levels and a default level of 80.

Fixes: e7733b42111c ("arm64: dts: qcom: Add support for Dell Inspiron 7441 / Latitude 7455")
Reported-by: Rafael Dettogni Guariento <rafael.guariento@xxxxxxx>
Tested-by: Rafael Dettogni Guariento <rafael.guariento@xxxxxxx>
Signed-off-by: Avalon Vargas <avalon.vargas.centeno@xxxxxxxxxxxxx>
---
Equivalent configurations have been tested on two Dell Inspiron 7441
units. Rafael tested this patch's resulting nodes on his stock DTB,
verified the live interpolated table, and confirmed brightness control,
Fn keys, no low-brightness flicker, and successful suspend/resume.
His Tested-by was supplied by direct email.

The 4266537 ns PWM period is borrowed from the upstream ThinkPad T14s
LCD configuration. It works on both tested units but has not been
measured from Dell firmware. Feedback on that choice is welcome.

Validation: strict checkpatch has only the missing public report URL
warning for Reported-by (the report was direct email). GCC/dtc DTB build
and dt-validate against this tree's bindings pass, with the same dtc
warnings as the unchanged base. The kernel dtbs_check target was not run.

This is scoped to the 7441. The earlier report of working AUX control
on a 7445 with the same panel model remains to be compared for platform,
EDID and DPCD differences.
---
 .../qcom/x1e80100-dell-inspiron-14-plus-7441.dts   | 32 ++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/x1e80100-dell-inspiron-14-plus-7441.dts b/arch/arm64/boot/dts/qcom/x1e80100-dell-inspiron-14-plus-7441.dts
index 75e10d97c..98632cccd 100644
--- a/arch/arm64/boot/dts/qcom/x1e80100-dell-inspiron-14-plus-7441.dts
+++ b/arch/arm64/boot/dts/qcom/x1e80100-dell-inspiron-14-plus-7441.dts
@@ -10,6 +10,19 @@
 / {
 	model = "Dell Inspiron 14 Plus 7441";
 	compatible = "dell,inspiron-14-plus-7441", "qcom,x1e80100";
+
+	backlight: backlight {
+		compatible = "pwm-backlight";
+		pwms = <&pmk8550_pwm 0 4266537>;
+		power-supply = <&vreg_edp_3p3>;
+
+		brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>;
+		num-interpolated-steps = <10>;
+		default-brightness-level = <80>;
+
+		pinctrl-0 = <&edp_bl_pwm>;
+		pinctrl-names = "default";
+	};
 };
 
 &sound {
@@ -42,6 +55,25 @@ &iris {
 	status = "okay";
 };
 
+&mdss_dp3 {
+	aux-bus {
+		panel {
+			backlight = <&backlight>;
+		};
+	};
+};
+
+&pmk8550_gpios {
+	edp_bl_pwm: edp-bl-pwm-state {
+		pins = "gpio5";
+		function = "func3";
+	};
+};
+
+&pmk8550_pwm {
+	status = "okay";
+};
+
 &remoteproc_adsp {
 	firmware-name = "qcom/x1e80100/dell/inspiron-14-plus-7441/qcadsp8380.mbn",
 			"qcom/x1e80100/dell/inspiron-14-plus-7441/adsp_dtbs.elf";

---
base-commit: 704340f1cd0dcef829eb62f5b48ae95a2ce17bdf
change-id: 20260918-dell7441-backlight-00212af0da18

Best regards,
--  
Avalon Vargas <avalon.vargas.centeno@xxxxxxxxxxxxx>