pwm-backlight: 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>
---
Changes since v1:
 - Also check if the regulator is enabled. If the power supply is disabled,
   and a phandle points to it, the backlight should stay powered down.
---
 drivers/video/backlight/pwm_bl.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index eff379b..31afd6d 100644
--- 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;
+	int initial_blank = FB_BLANK_UNBLANK;
+	bool phandle;
 	int ret;
 
 	if (!data) {

@@ -264,12 +266,32 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 		pb->enable_gpio = gpio_to_desc(data->enable_gpio);
 	}
 
+	phandle = of_find_property(pdev->dev.of_node, "phandle", NULL) != NULL;
+
+	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)) {
 		ret = PTR_ERR(pb->pwm);

@@ -321,6 +343,7 @@ 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);

-- 
2.1.4

Hi Thierry, Jingoo, Lee,

Am Donnerstag, den 30.07.2015, 19:22 +0200 schrieb Philipp Zabel:

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.

do you have any comments on this?

This patch fixes premature backlight illumination issues for DT probed
devices with enable gpio or regulator without changing the behavior of
the non-DT case or DT cases where the enable gpio and regulator are kept
initially enabled or where no other device node points to the backlight
via phandle.

regards
Philipp

23 more quoted lines

On Wed, 26 Aug 2015, Philipp Zabel wrote:

Hi Thierry, Jingoo, Lee,

Am Donnerstag, den 30.07.2015, 19:22 +0200 schrieb Philipp Zabel:

quoted

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.

do you have any comments on this?

This patch fixes premature backlight illumination issues for DT probed
devices with enable gpio or regulator without changing the behavior of
the non-DT case or DT cases where the enable gpio and regulator are kept
initially enabled or where no other device node points to the backlight
via phandle.

I need Thierry's review to move forward on this.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
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