On Tue, Oct 22, 2019 at 10:36:24AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
>
> The GPIO backlight driver currently requests the line 'as is', without
> acively setting its direction. This can lead to problems: if the line
> is in input mode by default, we won't be able to drive it later when
> updating the status and also reading its initial value doesn't make
> sense for backlight setting.
>
> Request the line 'as is' initially, so that we can read its value
> without affecting it but then change the direction to output explicitly
> when setting the initial brightness.
>
> Also: check the current direction and only read the value if it's output.
>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> ---
> drivers/video/backlight/gpio_backlight.c | 23 ++++++++++++++++++-----
> 1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
> index 3955b513f2f8..52f17c9ca1c3 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -25,9 +25,8 @@ struct gpio_backlight {
> int def_value;
> };
>
> -static int gpio_backlight_update_status(struct backlight_device *bl)
> +static int gpio_backlight_get_next_brightness(struct backlight_device *bl)
> {
> - struct gpio_backlight *gbl = bl_get_data(bl);
> int brightness = bl->props.brightness;
>
> if (bl->props.power != FB_BLANK_UNBLANK ||
> @@ -35,6 +34,14 @@ static int gpio_backlight_update_status(struct backlight_device *bl)
> bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
> brightness = 0;
>
> + return brightness;
> +}
> +
> +static int gpio_backlight_update_status(struct backlight_device *bl)
> +{
> + struct gpio_backlight *gbl = bl_get_data(bl);
> + int brightness = gpio_backlight_get_next_brightness(bl);
> +
> gpiod_set_value_cansleep(gbl->gpiod, brightness);
>
> return 0;
> @@ -85,7 +92,8 @@ static int gpio_backlight_initial_power_state(struct gpio_backlight *gbl)
> return gbl->def_value ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
>
> /* if the enable GPIO is disabled, do not enable the backlight */
> - if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
> + if (gpiod_get_direction(gbl->gpiod) == 0 &&
> + gpiod_get_value_cansleep(gbl->gpiod) == 0)
> return FB_BLANK_POWERDOWN;
>
> return FB_BLANK_UNBLANK;
> @@ -98,7 +106,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
> struct backlight_properties props;
> struct backlight_device *bl;
> struct gpio_backlight *gbl;
> - int ret;
> + int ret, init_brightness;
>
> gbl = devm_kzalloc(&pdev->dev, sizeof(*gbl), GFP_KERNEL);
> if (gbl == NULL)
> @@ -151,7 +159,12 @@ static int gpio_backlight_probe(struct platform_device *pdev)
> bl->props.power = gpio_backlight_initial_power_state(gbl);
> bl->props.brightness = 1;
>
> - backlight_update_status(bl);
> + init_brightness = gpio_backlight_get_next_brightness(bl);
> + ret = gpiod_direction_output(gbl->gpiod, init_brightness);
> + if (ret) {
> + dev_err(&pdev->dev, "failed to set initial brightness\n");
> + return ret;
> + }
>
> platform_set_drvdata(pdev, bl);
> return 0;
> --
> 2.23.0
>
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