[PATCH v5] 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>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
---
 - Rebased onto v4.4-rc1
 - Added Heiko's Tested-by
---
 drivers/video/backlight/pwm_bl.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index ae3c6b6..3daf9cc 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;
+	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);

-- 
2.6.2

On Wed, 18 Nov 2015, Philipp Zabel wrote:

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>
---
 - Rebased onto v4.4-rc1
 - Added Heiko's Tested-by
---
 drivers/video/backlight/pwm_bl.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

Applied, thanks.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog

Hi Lee,

On Wed, Nov 25, 2015 at 12:26 AM, Lee Jones [off-list ref] wrote:

On Wed, 18 Nov 2015, Philipp Zabel wrote:

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.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
---
 - Rebased onto v4.4-rc1
 - Added Heiko's Tested-by
---
 drivers/video/backlight/pwm_bl.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

Applied, thanks.

Hmm, where was this applied?  I do not see it in:
 * v4.4-rc4
 * linux-next next-20151203 (dcccebc - Add linux-next specific files
for 20151203)

Nor do I see it in any branch in:
 * git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight
Is this the right git?
By the way this repository has a git tag called "HEAD", which is a bit
annoying since every time I "git remote update" from here, git gets
confused until I manually delete it (git tag -d HEAD).

Thanks,
-Dan

On Mon, 07 Dec 2015, Daniel Kurtz wrote:

Hi Lee,

On Wed, Nov 25, 2015 at 12:26 AM, Lee Jones [off-list ref] wrote:

quoted

On Wed, 18 Nov 2015, Philipp Zabel wrote:

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.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
---
 - Rebased onto v4.4-rc1
 - Added Heiko's Tested-by
---
 drivers/video/backlight/pwm_bl.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

Applied, thanks.

Hmm, where was this applied?  I do not see it in:
 * v4.4-rc4
 * linux-next next-20151203 (dcccebc - Add linux-next specific files
for 20151203)

Nor do I see it in any branch in:
 * git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight
Is this the right git?

Yes, that's right.  When I say "applied", it means I applied it to my
local repository.  I am careful not to allude to the patch being
"pushed".  There is no guarantee when this will happen, since it
completly depends how busy the subsystem is.  For Backlight, as the
churn is low, the impetus for pushing is pretty low.

It has been "pushed" now though.

By the way this repository has a git tag called "HEAD", which is a bit
annoying since every time I "git remote update" from here, git gets
confused until I manually delete it (git tag -d HEAD).

Thanks for letting me know.  I have now removed this tag.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog