[PATCHv2] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero
From: Lothar Waßmann <hidden>
Date: 2016-06-07 10:14:08
Also in:
linux-devicetree, linux-pwm, lkml
Subsystem:
backlight class/subsystem, framebuffer layer, led subsystem, open firmware and flattened device tree bindings, the rest · Maintainers:
Lee Jones, Daniel Thompson, Jingoo Han, Helge Deller, Pavel Machek, Rob Herring, Krzysztof Kozlowski, Conor Dooley, Linus Torvalds
'brightness' is usually an index into a table of duty_cycle values, where the value at index 0 may well be non-zero (tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life examples). Thus brightness = 0 does not necessarily mean that the PWM output will be inactive. Check for 'duty_cycle = 0' rather than 'brightness = 0' to decide whether to disable the PWM. Signed-off-by: Lothar Waßmann <redacted> --- Changes wrt. v1: - update binding docs to reflect the change .../devicetree/bindings/leds/backlight/pwm-backlight.txt | 9 ++++++--- drivers/video/backlight/pwm_bl.c | 4 ++-- 2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
index 764db86..95fa8a9 100644
--- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt@@ -4,10 +4,13 @@ Required properties: - compatible: "pwm-backlight" - pwms: OF device-tree PWM specification (see PWM binding[0]) - 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. + are in the range from 0 to 255, but any range 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). + from these values. 0 means a 0% duty cycle, while the highest value in + the array represents a 100% duty cycle. + The range may be in reverse order (starting with the maximum duty cycle + value) to create a PWM signal with the 100% duty cycle representing + minimum and 0% duty cycle maximum brigthness. - default-brightness-level: the default brightness level (index into the array defined by the "brightness-levels" property) - power-supply: regulator for supply voltage
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index b2b366b..80b2b52 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c@@ -103,8 +103,8 @@ static int pwm_backlight_update_status(struct backlight_device *bl) if (pb->notify) brightness = pb->notify(pb->dev, brightness); - if (brightness > 0) { - duty_cycle = compute_duty_cycle(pb, brightness); + duty_cycle = compute_duty_cycle(pb, brightness); + if (duty_cycle > 0) { pwm_config(pb->pwm, duty_cycle, pb->period); pwm_backlight_power_on(pb, brightness); } else
--
2.1.4