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

[Alex Courbot <acourbot@nvidia.com>]

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@nvidia.com>
> ---
> 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.