Thierry Reding wrote at Tuesday, December 20, 2011 3:32 AM:

This commit adds very basic support for device-tree probing. Currently,
only a PWM and maximum and default brightness values can be specified.
Enabling or disabling backlight power via GPIOs is not yet supported.

+Required properties:
+  - compatible: "pwm-backlight"
+  - default-brightness: the default brightness setting
+  - max-brightness: the maximum brightness setting

What are the units of those two properties? Percentage seems like a
reasonable choice, although that's not what the patch implements.

+  - pwm: OF device-tree PWM specification
+
+Example:
+
+	backlight {
+		compatible = "pwm-backlight";
+		default-brightness = <224>;
+		max-brightness = <255>;
+		pwm = <&pwm 0 5000000>;
+	};

This may be fine, but I'm not sure that representing the backlight as a
standalone object is correct; I wonder if you want to represent a complete
LCD display complex, including backlight, various GPIOs, and other display
properties, all in the one node? That said, I suppose you could easily
layer this as follows:

reg: regulator {
    // GPIO regulator
};

bl: backlight {
    compatible = "pwm-backlight";
    default-brightness = <224>;
    max-brightness = <255>;
    pwm = <&pwm 0 5000000>;
    power-supply = <&reg>;
};

lcd@x {
    backlight = <&bl>;
    ...
};

so this probably is OK.

...

+static int pwm_backlight_parse_dt(struct device *dev,
+				  struct platform_pwm_backlight_data *data)

...

+	/*
+	 * TODO: Most users of this driver use a number of GPIOs to control
+	 *       backlight power. Support for specifying these needs to be
+	 *       added.
+	 */

At least for the power GPIO, this should probably modeled as a GPIO-based
fixed voltage regulator. Are there other GPIOs that are directly related
to a backlight rather than an LCD complex?

-- 
nvpublic