On 03/14/2012 09:56 AM, Thierry Reding wrote:

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

A pointer to the exit() callback is stored in the driver data to keep it
around until the driver is unloaded.

+pwm-backlight bindings
+
+Required properties:
+  - compatible: "pwm-backlight"
+  - pwm: OF device-tree PWM specification
+  - num-brightness-levels: number of distinct brightness levels
+  - brightness-levels: array of distinct brightness levels

I assume the values in this array are 0 (darkest/off) to 255 (max
brightness)? The doc should probably specify this.

+  - default-brightness-level: the default brightness level

Likewise, this is an index into the default-brightness-level? Again,
it'd be best to explicitly state this.

...

+		brightness-levels = <0 4 8 16 32 64 128 255>;
+		default-brightness-level = <6>;

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

...

+		ret = of_property_read_u32(node, "default-brightness-level",
+					   &value);
+		if (ret < 0)
+			goto free;

Range-check that against max_brightness?

 static int pwm_backlight_probe(struct platform_device *pdev)

...

-	pb->pwm = pwm_request(data->pwm_id, "backlight");
-	if (IS_ERR(pb->pwm)) {
-		dev_err(&pdev->dev, "unable to request PWM for backlight\n");
-		ret = PTR_ERR(pb->pwm);
-		goto err_alloc;
-	} else
-		dev_dbg(&pdev->dev, "got pwm for backlight\n");
+	if (!pb->pwm) {
+		pb->pwm = pwm_request(data->pwm_id, "backlight");
+		if (IS_ERR(pb->pwm)) {
+			dev_err(&pdev->dev, "unable to request PWM for backlight\n");
+			ret = PTR_ERR(pb->pwm);
+			goto err_alloc;
+		} else
+			dev_dbg(&pdev->dev, "got pwm for backlight\n");
+	}

Hmmm. It'd be more consistent if pwm_backlight_parse_dt() called
something like of_pwm_get() instead of of_pwm_request(), so that this
code could always call pwm_request() on the PWM and hence operate the
same irrespective of DT vs non-DT. GPIOs work that way at least.