From 0408fb4b34ab71680b60c8a02b52e8a2c054bb2e Mon Sep 17 00:00:00 2001 From: "Philip, Avinash" Date: Fri, 28 Sep 2012 10:20:20 +1000 Subject: [PATCH] pwm_backlight: add device tree support for Low Threshold Brightness Some backlights perform poorly when driven by a PWM with a short duty-cycle. For such devices, the low threshold can be used to specify a lower bound for the duty-cycle and should be chosen to exclude the problematic range. Add device tree probing support for platform_pwm_backlight_data,lth_brightness, putting low-threshold-brightness as the optional property's name. Signed-off-by: Philip, Avinash Cc: Thierry Reding Cc: Richard Purdie Cc: Florian Tobias Schandinat Cc: Grant Likely Signed-off-by: Andrew Morton --- .../bindings/video/backlight/pwm-backlight.txt | 10 ++++++++++ drivers/video/backlight/pwm_bl.c | 5 +++++ 2 files changed, 15 insertions(+) diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt index 1e4fc727f3b1..4e2991214e54 100644 --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt @@ -14,6 +14,15 @@ 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. Low threshold + brightness set to value so that backlight present on low end of + brightness. + Some panels, backlight would absent if duty percentage of PWM wave is less + than certain level (say 20%). By setting low-threshold-brightness to a + value above (percentage of brightness-levels max) 50 (20% of 255, if 255 + is max). On setting low-threshold-brightness, range of brightness-levels + is calculated in a region of low-threshold-brightness to brightness-levels + max. [0]: Documentation/devicetree/bindings/pwm/pwm.txt @@ -25,4 +34,5 @@ Example: brightness-levels = <0 4 8 16 32 64 128 255>; default-brightness-level = <6>; + low-threshold-brightness = <50>; }; diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 069983ca49ff..91ebf6f11087 100644 --- 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; } /* -- 2.39.5