backlight: gpio: Explicitly set the direction of the GPIO

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@baylibre.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

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;