[PATCH v4] backlight: gpio_backlight: Drop output GPIO direction check for initial power state

If GPIO pin is in input state but backlight is currently off due to
default pull downs, then initial power state is set to FB_BLANK_UNBLANK
in DT boot mode with phandle link and the backlight is effectively
turned on in gpio_backlight_probe(), which is undesirable according to
patch description of commit ec665b756e6f ("backlight: gpio-backlight:
Correct initial power state handling").

Quote:
---8<---
If in DT boot we have phandle link then leave the GPIO in a state which the
bootloader left it and let the user of the backlight to configure it further.
---8<---

So, let's drop output GPIO direction check and only check GPIO value to set
the initial power state.

Fixes: 706dc68102bc ("backlight: gpio: Explicitly set the direction of the GPIO")
Signed-off-by: Liu Ying <victor.liu@nxp.com>
---
v3->v4:
* Capitalize words 'gpio' in patch description. (Andy)
* Capitalize word 'gpio' in patch title.
* Quote appropriately in patch description. (Andy)

v2->v3:
* Add Fixes tag. (Daniel)

v1->v2:
* Improve patch description. (Daniel, Bartosz, Andy)

 drivers/video/backlight/gpio_backlight.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
index 6f78d928f054..38c46936fdcd 100644
--- a/drivers/video/backlight/gpio_backlight.c
+++ b/drivers/video/backlight/gpio_backlight.c

@@ -87,8 +87,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 		/* Not booted with device tree or no phandle link to the node */
 		bl->props.power = def_value ? FB_BLANK_UNBLANK
 					    : FB_BLANK_POWERDOWN;
-	else if (gpiod_get_direction(gbl->gpiod) == 0 &&
-		 gpiod_get_value_cansleep(gbl->gpiod) == 0)
+	else if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
 		bl->props.power = FB_BLANK_POWERDOWN;
 	else
 		bl->props.power = FB_BLANK_UNBLANK;

-- 
2.37.1

On Fri, Jul 21, 2023 at 09:29:03AM +0000, Ying Liu wrote:

If GPIO pin is in input state but backlight is currently off due to
default pull downs, then initial power state is set to FB_BLANK_UNBLANK
in DT boot mode with phandle link and the backlight is effectively
turned on in gpio_backlight_probe(), which is undesirable according to
patch description of commit ec665b756e6f ("backlight: gpio-backlight:
Correct initial power state handling").

Quote:
---8<---
If in DT boot we have phandle link then leave the GPIO in a state which the
bootloader left it and let the user of the backlight to configure it further.
---8<---

So, let's drop output GPIO direction check and only check GPIO value to set
the initial power state.

LGTM,
Reviewed-by: Andy Shevchenko <andy@kernel.org>

-- 
With Best Regards,
Andy Shevchenko

On Fri, Jul 21, 2023 at 11:29 AM Ying Liu [off-list ref] wrote:

Acked-by: Bartosz Golaszewski <redacted>

On Fri, Jul 21, 2023 at 11:29 AM Ying Liu [off-list ref] wrote:

If GPIO pin is in input state but backlight is currently off due to
default pull downs,

Oh what an interesting corner case!

then initial power state is set to FB_BLANK_UNBLANK
in DT boot mode with phandle link and the backlight is effectively
turned on in gpio_backlight_probe(), which is undesirable according to
patch description of commit ec665b756e6f ("backlight: gpio-backlight:
Correct initial power state handling").

Quote:
---8<---
If in DT boot we have phandle link then leave the GPIO in a state which the
bootloader left it and let the user of the backlight to configure it further.
---8<---

So, let's drop output GPIO direction check and only check GPIO value to set
the initial power state.

Fixes: 706dc68102bc ("backlight: gpio: Explicitly set the direction of the GPIO")
Signed-off-by: Liu Ying <victor.liu@nxp.com>

The solutions seems fine.
Acked-by: Linus Walleij <redacted>

Yours,
Linus Walleij

On Fri, 21 Jul 2023 09:29:03 +0000, Ying Liu wrote:

So, let's drop output GPIO direction check and only check GPIO value to set
the initial power state.

Applied, thanks!

[1/1] backlight: gpio_backlight: Drop output GPIO direction check for initial power state
      commit: fe1328b5b2a087221e31da77e617f4c2b70f3b7f

--
Lee Jones [李琼斯]