[PATCH] video: backlight: Only set maximum brightness for gpio-backlight

The note in c2adda27d202f ("video: backlight: Add of_find_backlight helper
in backlight.c") says that gpio-backlight uses brightness as power state.
Other backlight drivers do not, so limit this workaround to gpio-backlight.

This fixes the case where e.g. pwm-backlight can perfectly well be set to
brightness 0 on boot in DT, which without this patch leads to the display
brightness to be max instead of off.

Fixes: c2adda27d202f ("video: backlight: Add of_find_backlight helper in backlight.c")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel Thompson <redacted>
Cc: Meghana Madhyastha <redacted>
Cc: Noralf Trønnes <redacted>
Cc: Sean Paul <redacted>
Cc: Thierry Reding <redacted>
---
 drivers/video/backlight/backlight.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 537fe1b376ad7..dfb66171dec41 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c

@@ -676,6 +676,7 @@ EXPORT_SYMBOL(of_find_backlight_by_node);
 static struct backlight_device *of_find_backlight(struct device *dev)
 {
 	struct backlight_device *bd = NULL;
+	bool is_gpio_backlight = false;
 	struct device_node *np;
 
 	if (!dev)

@@ -685,6 +686,8 @@ static struct backlight_device *of_find_backlight(struct device *dev)
 		np = of_parse_phandle(dev->of_node, "backlight", 0);
 		if (np) {
 			bd = of_find_backlight_by_node(np);
+			is_gpio_backlight =
+				of_device_is_compatible(np, "gpio-backlight");
 			of_node_put(np);
 			if (!bd)
 				return ERR_PTR(-EPROBE_DEFER);

@@ -692,7 +695,7 @@ static struct backlight_device *of_find_backlight(struct device *dev)
 			 * Note: gpio_backlight uses brightness as
 			 * power state during probe
 			 */
-			if (!bd->props.brightness)
+			if (is_gpio_backlight && !bd->props.brightness)
 				bd->props.brightness = bd->props.max_brightness;
 		}
 	}

-- 
2.30.2

On Thu, Jul 08, 2021 at 11:10:58AM +0200, Marek Vasut wrote:

The note in c2adda27d202f ("video: backlight: Add of_find_backlight helper
in backlight.c") says that gpio-backlight uses brightness as power state.
Other backlight drivers do not, so limit this workaround to gpio-backlight.

This fixes the case where e.g. pwm-backlight can perfectly well be set to
brightness 0 on boot in DT, which without this patch leads to the display
brightness to be max instead of off.

Fixes: c2adda27d202f ("video: backlight: Add of_find_backlight helper in backlight.c")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel Thompson <redacted>
Cc: Meghana Madhyastha <redacted>
Cc: Noralf Trønnes <redacted>
Cc: Sean Paul <redacted>
Cc: Thierry Reding <redacted>

I have to admit that this patch really does makes it clear just how
nasty the hack in of_find_backlight() currently is.

Moreover I think it is also be obsolete. gpio-backlight power mode
handling was pretty broken when this code was introduced. It was fixed
in 2019 by ec665b756e6f ("backlight: gpio backlight: Correct initial
power state handling") by trying to match the behaviour of PWM
backlight.  The new code always sets the brightness to 1 so I think we
can just remove the hack from of_find_backlight() since I think it is
unreachable.


Daniel.

On 7/9/21 1:03 PM, Daniel Thompson wrote:

On Thu, Jul 08, 2021 at 11:10:58AM +0200, Marek Vasut wrote:

quoted

The note in c2adda27d202f ("video: backlight: Add of_find_backlight helper
in backlight.c") says that gpio-backlight uses brightness as power state.
Other backlight drivers do not, so limit this workaround to gpio-backlight.

This fixes the case where e.g. pwm-backlight can perfectly well be set to
brightness 0 on boot in DT, which without this patch leads to the display
brightness to be max instead of off.

Fixes: c2adda27d202f ("video: backlight: Add of_find_backlight helper in backlight.c")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel Thompson <redacted>
Cc: Meghana Madhyastha <redacted>
Cc: Noralf Trønnes <redacted>
Cc: Sean Paul <redacted>
Cc: Thierry Reding <redacted>

I have to admit that this patch really does makes it clear just how
nasty the hack in of_find_backlight() currently is.

Moreover I think it is also be obsolete. gpio-backlight power mode
handling was pretty broken when this code was introduced. It was fixed
in 2019 by ec665b756e6f ("backlight: gpio backlight: Correct initial
power state handling") by trying to match the behaviour of PWM
backlight.  The new code always sets the brightness to 1 so I think we
can just remove the hack from of_find_backlight() since I think it is
unreachable.

I assume by "new code" you mean the fixed gpio-backlight driver ?

Dropping the whole code after the Note: is fine by me.

Den 09.07.2021 15.19, skrev Marek Vasut:

On 7/9/21 1:03 PM, Daniel Thompson wrote:

quoted

On Thu, Jul 08, 2021 at 11:10:58AM +0200, Marek Vasut wrote:

quoted

The note in c2adda27d202f ("video: backlight: Add of_find_backlight
helper
in backlight.c") says that gpio-backlight uses brightness as power
state.
Other backlight drivers do not, so limit this workaround to
gpio-backlight.

This fixes the case where e.g. pwm-backlight can perfectly well be
set to
brightness 0 on boot in DT, which without this patch leads to the
display
brightness to be max instead of off.

Fixes: c2adda27d202f ("video: backlight: Add of_find_backlight helper
in backlight.c")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel Thompson <redacted>
Cc: Meghana Madhyastha <redacted>
Cc: Noralf Trønnes <redacted>
Cc: Sean Paul <redacted>
Cc: Thierry Reding <redacted>

I have to admit that this patch really does makes it clear just how
nasty the hack in of_find_backlight() currently is.

Moreover I think it is also be obsolete. gpio-backlight power mode
handling was pretty broken when this code was introduced. It was fixed
in 2019 by ec665b756e6f ("backlight: gpio backlight: Correct initial
power state handling") by trying to match the behaviour of PWM
backlight.  The new code always sets the brightness to 1 so I think we
can just remove the hack from of_find_backlight() since I think it is
unreachable.

I assume by "new code" you mean the fixed gpio-backlight driver ?

Dropping the whole code after the Note: is fine by me.

I haven't actually tested it, but when I saw the patch that Daniel
points to, it looked like this work around could be removed.
I haven't got time to tests it, but I will ack a patch that removes the
hack.

Noralf.