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().


Signed-off-by: Peter Ujfalusi <peter.ujfal...@ti.com>

for some reason the original patch got lost:

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


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

diff --git a/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 
                return PTR_ERR(bl);
- bl->props.brightness = gbl->def_value;
+       bl->props.power = gbl->def_value ? FB_BLANK_UNBLANK : 
+       bl->props.brightness = 1;
platform_set_drvdata(pdev, bl);

dri-devel mailing list

Reply via email to