Some back lights 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 lth_brightness putting
low-threshold-brightness as optional property.
Signed-off-by: Philip, Avinash <avinashphilip@xxxxxx>
---
Changes since v2:
- Added documentation part for configuring low-threshold-brightness
Changes since v1:
- Updated commit message.
- Changes to low-threshold-brightness.
- Merged example section to original.
:100644 100644 1e4fc72... 4e29912... M Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
:100644 100644 995f016... 29e6fe1... M drivers/video/backlight/pwm_bl.c
.../bindings/video/backlight/pwm-backlight.txt | 10 ++++++++++
drivers/video/backlight/pwm_bl.c | 5 +++++
2 files changed, 15 insertions(+), 0 deletions(-)
diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
index 1e4fc72..4e29912 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 995f016..29e6fe1 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;
}
/*
--
1.7.0.4
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