lkml.org 
[lkml]   [2018]   [Jun]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH RESEND] backlight: gpio-backlight: Correct initial power state handling
From
Date
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.


>
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
> ---
> 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);
>

\
 
 \ /
  Last update: 2018-06-13 17:12    [W:0.089 / U:3.584 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site