linux-kernel - Re: [PATCH 1/1] pwm_bl: Add support for backlight enable GPIO

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Message-ID: <20130304224611.GB17149@avionic-0098.mockup.avionic-design.de>
Date:	Mon, 4 Mar 2013 23:46:11 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Andrew Chew <achew@...dia.com>
Cc:	linux-kernel@...r.kernel.org, Alex Courbot <acourbot@...dia.com>
Subject: Re: [PATCH 1/1] pwm_bl: Add support for backlight enable GPIO

On Mon, Mar 04, 2013 at 01:49:49PM -0800, Andrew Chew wrote:
> The backlight enable GPIO is specified in the device tree node for
> backlight.
> 
> Signed-off-by: Andrew Chew <achew@...dia.com>
> ---
>  .../bindings/video/backlight/pwm-backlight.txt     |    2 ++
>  drivers/video/backlight/pwm_bl.c                   |   32 +++++++++++++++++---
>  include/linux/pwm_backlight.h                      |    2 ++
>  3 files changed, 32 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..f29f9c7 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;
> @@ -146,10 +149,15 @@ 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 +215,23 @@ 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");
> +		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 +240,7 @@ 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 +274,9 @@ 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 +291,8 @@ static int pwm_backlight_remove(struct platform_device *pdev)
>  	backlight_device_unregister(bl);
>  	pwm_config(pb->pwm, 0, pb->period);
>  	pwm_disable(pb->pwm);
> +	if (gpio_is_valid(pb->enable_gpio))
> +		gpio_free(pb->enable_gpio);
>  	if (pb->exit)
>  		pb->exit(&pdev->dev);
>  	return 0;
> diff --git a/include/linux/pwm_backlight.h b/include/linux/pwm_backlight.h
> index 56f4a86..2706805 100644
> --- a/include/linux/pwm_backlight.h
> +++ b/include/linux/pwm_backlight.h
> @@ -8,6 +8,8 @@
>  
>  struct platform_pwm_backlight_data {
>  	int pwm_id;
> +	int enable_gpio;
> +	unsigned int enable_gpio_flags;
>  	unsigned int max_brightness;
>  	unsigned int dft_brightness;
>  	unsigned int lth_brightness;

Hi Andrew,

I'm Cc'ing Alexandre Courbot, who has been working on supporting this in
a more generic way using power sequences. Generally this kind of support
really belongs in the common display framework, but I guess we could add
this one GPIO since it really is related only to the backlight. Usually
more than just an enable for the backlight is required so I'm not sure
how useful this really is.

Alex, any thought?

Thierry

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