linux-kernel - [PATCH 4/4] pwm_backlight: Add support for the whole range of the PWM in DT mode

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Date:	Tue, 22 Jan 2013 14:39:56 +0100
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Richard Purdie <rpurdie@...ys.net>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Landley <rob@...dley.net>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<devicetree-discuss@...ts.ozlabs.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-fbdev@...r.kernel.org>
Subject: [PATCH 4/4] pwm_backlight: Add support for the whole range of the PWM in DT mode

When booting with DT make it possible to use the whole range of the PWM when
controlling the backlight in a same way it is possible when the kernel is
booted in non DT mode.
A new property "max-brightness-level" can be used to specify the maximum
value the PWM can handle (time slots).
DTS files can use either the "brightness-levels" or the "max-brightness-level"
to configure the PWM.
In case both of these properties exist the driver will prefer the
"brightness-levels" over the "max-brightness-level".

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
---
 .../bindings/video/backlight/pwm-backlight.txt     | 12 +++++++++--
 drivers/video/backlight/pwm_bl.c                   | 24 ++++++++++++++--------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
index 1e4fc72..517924b 100644
--- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
@@ -3,13 +3,21 @@ pwm-backlight bindings
 Required properties:
   - compatible: "pwm-backlight"
   - pwms: OF device-tree PWM specification (see PWM binding[0])
+
+  Brightness range can be configured with either "brightness-levels" or with
+  "max-brightness-level".
   - brightness-levels: Array of distinct brightness levels. Typically these
       are in the range from 0 to 255, but any range starting at 0 will do.
       The actual brightness level (PWM duty cycle) will be interpolated
       from these values. 0 means a 0% duty cycle (darkest/off), while the
       last value in the array represents a 100% duty cycle (brightest).
-  - default-brightness-level: the default brightness level (index into the
-      array defined by the "brightness-levels" property)
+  - max-brightness-level: The maximum brightness level the PWM supports. When
+      the brightness is specified using this property the whole range from 0 to
+      "max-brightness-level" will be available to configure.
+  - default-brightness-level: the default brightness level. With
+      "brightness-levels" it is an index into the array defined by the
+      "brightness-levels" property. When it is used with "max-brightness-level"
+      it is the value in the range from 0 to "max-brightness-level"
 
 Optional properties:
   - pwm-names: a list of names for the PWM devices specified in the
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index df2d115..c0e4bc7 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -111,10 +111,17 @@ static int pwm_backlight_parse_dt(struct device *dev,
 
 	/* determine the number of brightness levels */
 	prop = of_find_property(node, "brightness-levels", &num_levels);
-	if (!prop)
-		return -EINVAL;
+	if (!prop) {
+		/* Levels not provided, look for the maximum property */
+		ret = of_property_read_u32(node, "max-brightness-level",
+					   &value);
+		if (ret < 0)
+			return ret;
 
-	num_levels /= sizeof(u32);
+		data->max_brightness = value;
+	} else {
+		num_levels /= sizeof(u32);
+	}
 
 	/* read brightness levels from DT property */
 	if (num_levels > 0) {
@@ -130,14 +137,13 @@ static int pwm_backlight_parse_dt(struct device *dev,
 			return ret;
 
 		data->max_brightness = num_levels;
+	}
 
-		ret = of_property_read_u32(node, "default-brightness-level",
-					   &value);
-		if (ret < 0)
-			return ret;
+	ret = of_property_read_u32(node, "default-brightness-level", &value);
+	if (ret < 0)
+		return ret;
 
-		data->dft_brightness = value;
-	}
+	data->dft_brightness = value;
 
 	/*
 	 * TODO: Most users of this driver use a number of GPIOs to control
-- 
1.8.1.1

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