Re: [PATCH] backlight: led_bl: fix initial power state

Sam Ravnborg
2023-07-04T17:07:39Z

Hi Daniel,

> > @@ -200,8 +200,8 @@ static int led_bl_probe(struct platform_device *pdev)
> > props.type = BACKLIGHT_RAW;
> > props.max_brightness = priv->max_brightness;
> > props.brightness = priv->default_brightness;
> > - props.power = (priv->default_brightness > 0) ? FB_BLANK_POWERDOWN :
> > - FB_BLANK_UNBLANK;
> > + props.power = (priv->default_brightness > 0) ? FB_BLANK_UNBLANK :
> > + FB_BLANK_POWERDOWN;
>
> The logic was wrong before but I think will still be wrong after the
> change too (e.g. the bogus logic is probably avoiding backlight flicker
> in some use cases).
>
> The logic here needs to be similar to what pwm_bl.c implements in
> pwm_backlight_initial_power_state(). Whilst it might be better
> to implement this in led_bl_get_leds() let me show what I mean
> in code that fits in the current line:
>
> /*
> * Activate the backlight if the LEDs are already lit *or*
> * there is no phandle link (meaning the backlight power
> * state cannot be synced with the display state).
> */
> props.power = (active_at_boot || !dev->node->phandle) ?
> FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
>
The following code does the same using helpers:

if (active_at_boot || !dev->node->phandle))
backlight_enable(bd);
else
backlight_disable(bd);

The code needs to execute after backlight_device_register() so maybe not
so great an idea?!?

Sam