video: backlight: pwm-backlight: add a forced display hold off time o…

…ption

Add a possibility to force a display/backlight to be switched off for
a specified time. This is useful for displays which go nuts when the
off time is to short or the power-on sequence is not as expected.

Signed-off-by: Peter Fink <pfink@christ-es.de>

Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt

@@ -21,6 +21,10 @@ Optional properties:
   - pwm-off-delay-ms: Delay in ms between disabling the backlight using GPIO
                       (and setting PWM value to 0 at the same time) and
                       switching off the enable-display-gpio.
+  - display-hold-off-ms: Time in ms which the display enable gpio is forced off
+                         even if the backlight is switched on immediately after
+                         it has been turned off. This can be used if the
+                         display is not able to cope with fast on-off-on cycles.
   - 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)
@@ -52,6 +56,7 @@ Example:
 		enable-backlight-gpios = <&gpio 60 0>;
 		post-pwm-on-delay-ms = <10>;
 		pwm-off-delay-ms = <10>;
+		display-hold-off-ms = <20>;
 	};
 
 Example using num-interpolation-steps:

drivers/video/backlight/pwm_bl.c

@@ -39,6 +39,7 @@ struct pwm_bl_data {
 	bool			legacy;
 	unsigned int		pwm_on_delay;
 	unsigned int		pwm_off_delay;
+	unsigned int		hold_off_delay;
 	int			(*notify)(struct device *,
 					  int brightness);
 	void			(*notify_after)(struct device *,
@@ -91,6 +92,9 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
 
 	regulator_disable(pb->power_supply);
 	pb->enabled = false;
+
+	if (pb->hold_off_delay)
+		msleep(pb->hold_off_delay);
 }
 
 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
@@ -388,6 +392,7 @@ static int pwm_backlight_parse_dt(struct device *dev,
 	of_property_read_u32(node, "pwm-on-delay-ms",
 			     &data->pwm_on_delay);
 	of_property_read_u32(node, "pwm-off-delay-ms", &data->pwm_off_delay);
+	of_property_read_u32(node, "display-hold-off-ms", &data->hold_off_delay);
 
 	data->dp_enable_gpio = -EINVAL;
 	data->bl_enable_gpio = -EINVAL;
@@ -493,6 +498,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	pb->enabled = false;
 	pb->pwm_on_delay = data->pwm_on_delay;
 	pb->pwm_off_delay = data->pwm_off_delay;
+	pb->hold_off_delay = data->hold_off_delay;
 
 	pb->dp_enable_gpio = devm_gpiod_get_optional(&pdev->dev,
 						  "display-enable", GPIOD_ASIS);

include/linux/pwm_backlight.h

@@ -16,6 +16,7 @@ struct platform_pwm_backlight_data {
 	unsigned int *levels;
 	unsigned int pwm_on_delay;
 	unsigned int pwm_off_delay;
+	unsigned int hold_off_delay;
 	/* TODO remove once all users are switched to gpiod_* API */
 	int dp_enable_gpio;
 	int bl_enable_gpio;