drivers/video/backlight/pwm_bl.c: add device tree support for Low Threshold Brightness

Low Threshold Brightness should be configured to have a linear relation in
brightness scale.  This patch adds device tree support for low threshold
brightness as optional one for pwm_backlight.

Signed-off-by: Philip, Avinash <avinashphilip@ti.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
index 1e4fc727f3b180f84242a3d77b3854ad113b4a60..689c7d25f750de5bdb124f754484aac23d614767 100644 (file)
--- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
@@ -14,6 +14,8 @@ Required properties:
 Optional properties:
   - pwm-names: a list of names for the PWM devices specified in the
                "pwms" property (see PWM binding[0])
+  - low_threshold_brightness: brightness threshold low level. (get linear
+                scales in brightness in low end of brightness levels)
 
 [0]: Documentation/devicetree/bindings/pwm/pwm.txt
 
@@ -26,3 +28,22 @@ Example:
                brightness-levels = <0 4 8 16 32 64 128 255>;
                default-brightness-level = <6>;
        };
+
+Example for brightness_threshold_level:
+
+       backlight {
+               compatible      = "pwm-backlight";
+               pwms = <&pwm 0 50000>;
+
+               brightness-levels = <0 4 8 16 32 64 128 255>;
+               default-brightness-level = <6>;
+               low_threshold_brightness = <50>;
+       };
+};
+Note:
+Low threshold support is required to have linear brightness scale from
+0 to max. For some panels, backlight absent on low end of brightness
+scale. So support for Low Threshold been required. So that the scale of
+brightness changed from Low Threshold to Max in scales defined in
+brightness-levels. In this example 20% maximum brightness scale should
+be required to turn on panel backlight.

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 995f0164c9b082c7da2836123adfcb2b7f10a6c7..4965408502df1666c77ea8727bcb570eae90d68e 100644 (file)
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -143,6 +143,11 @@ static int pwm_backlight_parse_dt(struct device *dev,
 
                data->dft_brightness = value;
                data->max_brightness--;
+
+               ret = of_property_read_u32(node, "low_threshold_brightness",
+                                          &value);
+               if (!ret)
+                       data->lth_brightness = value;
        }
 
        /*