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    Subject[PATCH 1/1 v2] pwm_bl: Add support for backlight enable GPIO
    Date
    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);
    } 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");
    + 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);
    if (pb->notify_after)
    pb->notify_after(pb->dev, 0);
    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;
    --
    1.7.9.5


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