backlight: pwm_bl: Avoid backlight flicker when probed from DT

If the driver is probed from the device tree, and there is a phandle
property set on it, and the enable GPIO is already configured as output,
and the backlight is currently disabled, keep it disabled.
If all these conditions are met, assume there will be some other driver
that can enable the backlight at the appropriate time.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index ae3c6b6fd5db1e50e2eb74176f9cb5ef01805bb9..3daf9cc9bc3127cd2f0da4a63f5ce91ecb487448 100644 (file)
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -199,6 +199,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
        struct backlight_properties props;
        struct backlight_device *bl;
        struct pwm_bl_data *pb;
+       phandle phandle = pdev->dev.of_node->phandle;
+       int initial_blank = FB_BLANK_UNBLANK;
        int ret;
 
        if (!data) {
@@ -242,7 +244,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
        pb->enabled = false;
 
        pb->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
-                                                 GPIOD_OUT_HIGH);
+                                                 GPIOD_ASIS);
        if (IS_ERR(pb->enable_gpio)) {
                ret = PTR_ERR(pb->enable_gpio);
                goto err_alloc;
@@ -264,12 +266,30 @@ static int pwm_backlight_probe(struct platform_device *pdev)
                pb->enable_gpio = gpio_to_desc(data->enable_gpio);
        }
 
+       if (pb->enable_gpio) {
+               /*
+                * If the driver is probed from the device tree and there is a
+                * phandle link pointing to the backlight node, it is safe to
+                * assume that another driver will enable the backlight at the
+                * appropriate time. Therefore, if it is disabled, keep it so.
+                */
+               if (phandle &&
+                   gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT &&
+                   gpiod_get_value(pb->enable_gpio) == 0)
+                       initial_blank = FB_BLANK_POWERDOWN;
+               else
+                       gpiod_direction_output(pb->enable_gpio, 1);
+       }
+
        pb->power_supply = devm_regulator_get(&pdev->dev, "power");
        if (IS_ERR(pb->power_supply)) {
                ret = PTR_ERR(pb->power_supply);
                goto err_alloc;
        }
 
+       if (phandle && !regulator_is_enabled(pb->power_supply))
+               initial_blank = FB_BLANK_POWERDOWN;
+
        pb->pwm = devm_pwm_get(&pdev->dev, NULL);
        if (IS_ERR(pb->pwm) && PTR_ERR(pb->pwm) != -EPROBE_DEFER
            && !pdev->dev.of_node) {
@@ -320,6 +340,7 @@ static int pwm_backlight_probe(struct platform_device *pdev)
        }
 
        bl->props.brightness = data->dft_brightness;
+       bl->props.power = initial_blank;
        backlight_update_status(bl);
 
        platform_set_drvdata(pdev, bl);