[PATCH RESEND] backlight: gpio-backlight: Correct initial power state handling

The default-on property - or the def_value via legacy pdata) should be
handled as:
if it is 1, the backlight must be enabled (kept enabled)
if it is 0, the backlight must be disabled (kept disabled)

This only works for the case when default-on is set. If it is not set then
the brightness of the backlight is set to 0. Now if the backlight is
enabled by external driver (graphics) the backlight will stay disabled since
the brightness is configured as 0. The backlight will not turn on.

The correct action at probe time is to configure the props.power to
FB_BLANK_UNBLANK if we want the backlight on by default or to
FB_BLANK_POWERDOWN if the backlight should be off by default.

The initial brightness should be set to 1.

Signed-off-by: Peter Ujfalusi <redacted>
---
Hi,

for some reason the original patch got lost:
https://patchwork.kernel.org/patch/9445539/

But it is still valid, so I'm resending it.

Regards,
Peter

 drivers/video/backlight/gpio_backlight.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
index e470da95d806..904a4462cefe 100644
--- a/drivers/video/backlight/gpio_backlight.c
+++ b/drivers/video/backlight/gpio_backlight.c

@@ -142,7 +142,9 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 		return PTR_ERR(bl);
 	}
 
-	bl->props.brightness = gbl->def_value;
+	bl->props.power = gbl->def_value ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
+	bl->props.brightness = 1;
+
 	backlight_update_status(bl);
 
 	platform_set_drvdata(pdev, bl);

-- 
Peter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

On 08/05/18 08:04, Peter Ujfalusi wrote:

The default-on property - or the def_value via legacy pdata) should be
handled as:
if it is 1, the backlight must be enabled (kept enabled)
if it is 0, the backlight must be disabled (kept disabled)

This only works for the case when default-on is set. If it is not set then
the brightness of the backlight is set to 0. Now if the backlight is
enabled by external driver (graphics) the backlight will stay disabled since
the brightness is configured as 0. The backlight will not turn on.

The correct action at probe time is to configure the props.power to
FB_BLANK_UNBLANK if we want the backlight on by default or to
FB_BLANK_POWERDOWN if the backlight should be off by default.

The initial brightness should be set to 1.

Hmnn... I guess this comes down to the definition of "on" for a binary

Actually I'm a little worried that backlight already has too many 
different behaviors and that this patch introduces another way for them 
to be different!

Is there any mileage in adopting the same approach as PWM backlight for 
blank/unblank management as a way to get a flicker free boot?

For PWM the default property controls the initial brightness and the 
initial power state is unblanked *unless* there is a phandle link to the 
node, in which case we inherit whatever the power state the bootloader 
had configured before the driver probed.

Put another way, what happens is we implement 
gpio_backlight_initial_power_state() to perform a similar task to 
pwm_backlight_initial_power_state().


Daniel.

Daniel,

On 2018-06-13 18:11, Daniel Thompson wrote:

On 08/05/18 08:04, Peter Ujfalusi wrote:

quoted

The default-on property - or the def_value via legacy pdata) should be
handled as:
if it is 1, the backlight must be enabled (kept enabled)
if it is 0, the backlight must be disabled (kept disabled)

This only works for the case when default-on is set. If it is not set
then
the brightness of the backlight is set to 0. Now if the backlight is
enabled by external driver (graphics) the backlight will stay disabled
since
the brightness is configured as 0. The backlight will not turn on.

The correct action at probe time is to configure the props.power to
FB_BLANK_UNBLANK if we want the backlight on by default or to
FB_BLANK_POWERDOWN if the backlight should be off by default.

The initial brightness should be set to 1.

Hmnn... I guess this comes down to the definition of "on" for a binary

Actually I'm a little worried that backlight already has too many
different behaviors and that this patch introduces another way for them
to be different!

Is there any mileage in adopting the same approach as PWM backlight for
blank/unblank management as a way to get a flicker free boot?

This patch is merely fixing a bug in the driver.

For PWM the default property controls the initial brightness and the
initial power state is unblanked *unless* there is a phandle link to the
node, in which case we inherit whatever the power state the bootloader
had configured before the driver probed.

Put another way, what happens is we implement
gpio_backlight_initial_power_state() to perform a similar task to
pwm_backlight_initial_power_state().

I agree, but what should we do with the default-on parameter?

non DT boot or DT boot, no phandle link:
default-on ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN

DT boot and phandle link:
if the GPIO was enabled by the bootloader: FB_BLANK_UNBLANK
if the GIOP was not enabled by the bootloader: FB_BLANK_POWERDOWN

I think this will mimic closely what the
pwm_backlight_initial_power_state() does.

- Péter

Daniel.

quoted

Signed-off-by: Peter Ujfalusi <redacted>
---
Hi,

for some reason the original patch got lost:
https://patchwork.kernel.org/patch/9445539/

But it is still valid, so I'm resending it.

Regards,
Peter

  drivers/video/backlight/gpio_backlight.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/gpio_backlight.c

b/drivers/video/backlight/gpio_backlight.c
index e470da95d806..904a4462cefe 100644

--- a/drivers/video/backlight/gpio_backlight.c
+++ b/drivers/video/backlight/gpio_backlight.c

@@ -142,7 +142,9 @@ static int gpio_backlight_probe(struct

platform_device *pdev)
          return PTR_ERR(bl);
      }
  -    bl->props.brightness = gbl->def_value;
+    bl->props.power = gbl->def_value ? FB_BLANK_UNBLANK :
FB_BLANK_POWERDOWN;
+    bl->props.brightness = 1;
+
      backlight_update_status(bl);
        platform_set_drvdata(pdev, bl);

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki