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.
> diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight
> +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 = <®>;
};
lcd@x {
backlight = <&bl>;
...
};
so this probably is OK.
> diff --git a/drivers/video/backlight/pwm_bl.c
> b/drivers/video/backlight/pwm_bl.c
...
> +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?
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