linux-kernel - [PATCH v3 2/3] arm64: dts: qcom: trogdor: Add brightness-levels

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Date:   Wed, 21 Oct 2020 22:04:44 -0700
From:   Alexandru Stan <amstan@...omium.org>
To:     Heiko Stuebner <heiko@...ech.de>, Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Alexandru Stan <amstan@...omium.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 2/3] arm64: dts: qcom: trogdor: Add brightness-levels

We want userspace to represent the human perceived brightness.
Since the led drivers and the leds themselves don't have a
linear response to the value we give them in terms of perceived
brightness, we'll bake the curve into the dts.

The panel also doesn't have a good response under 5%, so we'll avoid
sending it anything lower than that.

Note: Ideally this patch should be coupled with the driver change from
"backlight: pwm_bl: Fix interpolation", but it can work without it,
without looking too ugly.

Signed-off-by: Alexandru Stan <amstan@...omium.org>
---

 arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
index bf875589d364..ccdabc6c4994 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
@@ -179,6 +179,15 @@ pp3300_fp_tp: pp3300-fp-tp-regulator {
 	backlight: backlight {
 		compatible = "pwm-backlight";
 
+		/* The panels don't seem to like anything below ~ 5% */
+		brightness-levels = <
+			196 256 324 400 484 576 676 784 900 1024 1156 1296
+			1444 1600 1764 1936 2116 2304 2500 2704 2916 3136
+			3364 3600 3844 4096
+		>;
+		num-interpolated-steps = <64>;
+		default-brightness-level = <951>;
+
 		pwms = <&cros_ec_pwm 1>;
 		enable-gpios = <&tlmm 12 GPIO_ACTIVE_HIGH>;
 		power-supply = <&ppvar_sys>;
-- 
2.28.0