[PATCH V3 2/2] pwm_bl: Add mandatory backlight enable regulator

[Andrew Chew <achew@nvidia.com>]

Many backlights need to be explicitly enabled.  Typically, this is done
with a GPIO.  For flexibility, we generalize the enable mechanism to a
regulator.

If an enable regulator is not needed, then a dummy regulator can be given
to the backlight driver.  If a GPIO is used to enable the backlight,
then a fixed regulator can be instantiated to control the GPIO.

The backlight enable regulator can be specified in the device tree node
for the backlight, or can be done with legacy board setup code in the
usual way.

Signed-off-by: Andrew Chew <achew@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
---
Minor modification to pwm_backlight_enable() and pwm_backlight_disable(),
to keep the error value of the regulator call and report the error value
in the case of an error, from Peter and Thierry's feedback.  Used "ret"
to be consistent with the rest of the driver.

 .../bindings/video/backlight/pwm-backlight.txt     |   14 +++++
 drivers/video/backlight/pwm_bl.c                   |   59 ++++++++++++++++----
 2 files changed, 63 insertions(+), 10 deletions(-)

diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
index 1e4fc72..7e2e089 100644
--- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
@@ -10,6 +10,11 @@ Required properties:
       last value in the array represents a 100% duty cycle (brightest).
   - default-brightness-level: the default brightness level (index into the
       array defined by the "brightness-levels" property)
+  - enable-supply: A phandle to the regulator device tree node. This
+      regulator will be turned on and off as the pwm is enabled and disabled.
+      Many backlights are enabled via a GPIO. In this case, we instantiate
+      a fixed regulator and give that to enable-supply. If a regulator
+      is not needed, then provide a dummy fixed regulator.
 
 Optional properties:
   - pwm-names: a list of names for the PWM devices specified in the
@@ -19,10 +24,19 @@ Optional properties:
 
 Example:
 
+	bl_en: fixed-regulator {
+                compatible = "regulator-fixed";
+                regulator-name = "bl-en-supply";
+                regulator-boot-on;
+                gpio = <&some_gpio>;
+                enable-active-high;
+	};
+
 	backlight {
 		compatible = "pwm-backlight";
 		pwms = <&pwm 0 5000000>;
 
 		brightness-levels = <0 4 8 16 32 64 128 255>;
 		default-brightness-level = <6>;
+		enable-supply = <&bl_en>;
 	};
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 1fea627..e4922f5 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -20,10 +20,13 @@
 #include <linux/pwm.h>
 #include <linux/pwm_backlight.h>
 #include <linux/slab.h>
+#include <linux/regulator/consumer.h>
 
 struct pwm_bl_data {
 	struct pwm_device	*pwm;
 	struct device		*dev;
+	bool			enabled;
+	struct regulator	*enable_supply;
 	unsigned int		period;
 	unsigned int		lth_brightness;
 	unsigned int		*levels;
@@ -35,6 +38,42 @@ struct pwm_bl_data {
 	void			(*exit)(struct device *);
 };
 
+static void pwm_backlight_enable(struct backlight_device *bl)
+{
+	struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
+	int ret;
+
+	/* Bail if we are already enabled. */
+	if (pb->enabled)
+		return;
+
+	pwm_enable(pb->pwm);
+
+	ret = regulator_enable(pb->enable_supply);
+	if (ret)
+		dev_warn(&bl->dev, "Failed to enable regulator: %d", ret);
+
+	pb->enabled = true;
+}
+
+static void pwm_backlight_disable(struct backlight_device *bl)
+{
+	struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
+	int ret;
+
+	/* Bail if we are already disabled. */
+	if (!pb->enabled)
+		return;
+
+	ret = regulator_disable(pb->enable_supply);
+	if (ret)
+		dev_warn(&bl->dev, "Failed to disable regulator: %d", ret);
+
+	pwm_disable(pb->pwm);
+
+	pb->enabled = false;
+}
+
 static int pwm_backlight_update_status(struct backlight_device *bl)
 {
 	struct pwm_bl_data *pb = bl_get_data(bl);
@@ -51,7 +90,7 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
 
 	if (brightness == 0) {
 		pwm_config(pb->pwm, 0, pb->period);
-		pwm_disable(pb->pwm);
+		pwm_backlight_disable(bl);
 	} else {
 		int duty_cycle;
 
@@ -65,7 +104,7 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
 		duty_cycle = pb->lth_brightness +
 		     (duty_cycle * (pb->period - pb->lth_brightness) / max);
 		pwm_config(pb->pwm, duty_cycle, pb->period);
-		pwm_enable(pb->pwm);
+		pwm_backlight_enable(bl);
 	}
 
 	if (pb->notify_after)
@@ -138,12 +177,6 @@ static int pwm_backlight_parse_dt(struct device *dev,
 		data->max_brightness--;
 	}
 
-	/*
-	 * TODO: Most users of this driver use a number of GPIOs to control
-	 *       backlight power. Support for specifying these needs to be
-	 *       added.
-	 */
-
 	return 0;
 }
 
@@ -206,6 +239,12 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	pb->exit = data->exit;
 	pb->dev = &pdev->dev;
 
+	pb->enable_supply = devm_regulator_get(&pdev->dev, "enable");
+	if (IS_ERR(pb->enable_supply)) {
+		ret = PTR_ERR(pb->enable_supply);
+		goto err_alloc;
+	}
+
 	pb->pwm = devm_pwm_get(&pdev->dev, NULL);
 	if (IS_ERR(pb->pwm)) {
 		dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
@@ -268,7 +307,7 @@ static int pwm_backlight_remove(struct platform_device *pdev)
 
 	backlight_device_unregister(bl);
 	pwm_config(pb->pwm, 0, pb->period);
-	pwm_disable(pb->pwm);
+	pwm_backlight_disable(bl);
 	if (pb->exit)
 		pb->exit(&pdev->dev);
 	return 0;
@@ -283,7 +322,7 @@ static int pwm_backlight_suspend(struct device *dev)
 	if (pb->notify)
 		pb->notify(pb->dev, 0);
 	pwm_config(pb->pwm, 0, pb->period);
-	pwm_disable(pb->pwm);
+	pwm_backlight_disable(bl);
 	if (pb->notify_after)
 		pb->notify_after(pb->dev, 0);
 	return 0;
-- 
1.7.9.5