Re: [PATCH 1/1 v2] pwm_bl: Add support for backlight enable GPIO

From: Alex Courbot
Date: Tue Mar 05 2013 - 00:14:43 EST

On 03/05/2013 01:43 PM, Andrew Chew wrote:
The backlight enable GPIO is specified in the device tree node for
backlight.

Signed-off-by: Andrew Chew <achew@xxxxxxxxxx>
---
I decided to go ahead with disabling/enabling the backlight via GPIO as
needed. Note that I named the new functions pwm_backlight_enable() and
pwm_backlight_disable() (instead of something more gpio-specific) because
I thought it would be convenient to have a generic hook for when someone
wants to add yet more stuff to be done on enable/disable.

I tested this by going into /sys/class/backlight/backlight.n and manually
adjusting the brightness, and checked the gpio state to see that it had
the appropriate value.

.../bindings/video/backlight/pwm-backlight.txt | 2 +
drivers/video/backlight/pwm_bl.c | 50 ++++++++++++++++++--
include/linux/pwm_backlight.h | 2 +
3 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
index 1e4fc72..1ed4f0f 100644
--- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
@@ -14,6 +14,8 @@ Required properties:
Optional properties:
- pwm-names: a list of names for the PWM devices specified in the
"pwms" property (see PWM binding[0])
+ - enable-gpio: a GPIO that needs to be used to enable the backlight
+ - enable-gpio-active-high: polarity of GPIO is active high (default is low)

[0]: Documentation/devicetree/bindings/pwm/pwm.txt

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 069983c..7dd426e 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/of_gpio.h>

struct pwm_bl_data {
struct pwm_device *pwm;
struct device *dev;
+ int enable_gpio;
+ unsigned int enable_gpio_flags;
unsigned int period;
unsigned int lth_brightness;
unsigned int *levels;
@@ -35,6 +38,20 @@ struct pwm_bl_data {
void (*exit)(struct device *);
};

+static void pwm_backlight_enable(struct pwm_bl_data *pb)
+{
+ if (gpio_is_valid(pb->enable_gpio))
+ gpio_set_value(pb->enable_gpio,
+ pb->enable_gpio_flags & GPIOF_INIT_HIGH ? 1 : 0);
+}
+
+static void pwm_backlight_disable(struct pwm_bl_data *pb)
+{
+ if (gpio_is_valid(pb->enable_gpio))
+ gpio_set_value(pb->enable_gpio,
+ pb->enable_gpio_flags & GPIOF_INIT_HIGH ? 0 : 1);
+}
+
static int pwm_backlight_update_status(struct backlight_device *bl)
{
struct pwm_bl_data *pb = dev_get_drvdata(&bl->dev);
@@ -53,6 +70,7 @@ 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(pb);

Maybe move the call to pwm_backlight_disable() before pwm_disable() to have a correctly nested power sequence?

Actually every call to pwm_disable/enable is near pwm_backlight_disable/enable, so you might as well want to call pwm_disable/enable within pwm_backlight_enable/disable to make the code more bullet-proof.

} else {
int duty_cycle;

@@ -67,6 +85,7 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
(duty_cycle * (pb->period - pb->lth_brightness) / max);
pwm_config(pb->pwm, duty_cycle, pb->period);
pwm_enable(pb->pwm);
+ pwm_backlight_enable(pb);
}

if (pb->notify_after)
@@ -146,10 +165,15 @@ static int pwm_backlight_parse_dt(struct device *dev,
}

/*
- * TODO: Most users of this driver use a number of GPIOs to control
- * backlight power. Support for specifying these needs to be
- * added.
+ * If "enable-gpio" is present, use that GPIO to enable the backlight.
+ * The presence (or not) of "enable-gpio-active-high" will determine
+ * the value of the GPIO.
*/
+ data->enable_gpio = of_get_named_gpio(node, "enable-gpio", 0);
+ if (of_property_read_bool(node, "enable-gpio-active-high"))
+ data->enable_gpio_flags = GPIOF_OUT_INIT_HIGH;
+ else
+ data->enable_gpio_flags = GPIOF_OUT_INIT_LOW;

return 0;
}
@@ -207,12 +231,23 @@ static int pwm_backlight_probe(struct platform_device *pdev)
} else
max = data->max_brightness;

+ pb->enable_gpio = data->enable_gpio;
+ pb->enable_gpio_flags = data->enable_gpio_flags;
pb->notify = data->notify;
pb->notify_after = data->notify_after;
pb->check_fb = data->check_fb;
pb->exit = data->exit;
pb->dev = &pdev->dev;

+ if (gpio_is_valid(pb->enable_gpio)) {
+ ret = gpio_request_one(pb->enable_gpio,
+ GPIOF_DIR_OUT | pb->enable_gpio_flags, "bl_en");

I would not assume that the backlight should be enabled here. Maybe you can use gpio_request() and gpio_set_output() to leave the output value unchanged - the backlight framework will call update_status() anyway, which will set the GPIO value accordingly.

+ if (ret) {
+ dev_err(&pdev->dev, "failed to allocate bl_en gpio");
+ 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");
@@ -221,7 +256,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
if (IS_ERR(pb->pwm)) {
dev_err(&pdev->dev, "unable to request legacy PWM\n");
ret = PTR_ERR(pb->pwm);
- goto err_alloc;
+ goto err_gpio;
}
}

@@ -255,6 +290,9 @@ static int pwm_backlight_probe(struct platform_device *pdev)
platform_set_drvdata(pdev, bl);
return 0;

+err_gpio:
+ if (gpio_is_valid(data->enable_gpio))
+ gpio_free(data->enable_gpio);
err_alloc:
if (data->exit)
data->exit(&pdev->dev);
@@ -269,6 +307,9 @@ 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(pb);
+ if (gpio_is_valid(pb->enable_gpio))
+ gpio_free(pb->enable_gpio);
if (pb->exit)
pb->exit(&pdev->dev);
return 0;
@@ -284,6 +325,7 @@ static int pwm_backlight_suspend(struct device *dev)
pb->notify(pb->dev, 0);
pwm_config(pb->pwm, 0, pb->period);
pwm_disable(pb->pwm);
+ pwm_backlight_disable(pb);

Another good reason to move pwm_disable inside pwm_backlight_disable. :)

Alex.

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