Hi Daniel,
On Thursday, July 20, 2023 7:28 PM Daniel Thompson <daniel.thompson@xxxxxxxxxx> wrote:
>
> On Thu, Jul 20, 2023 at 06:06:27AM +0000, Ying Liu wrote:
> > Bootloader may leave gpio direction as input and gpio value as logical low.
> > It hints that initial backlight power state should be
> FB_BLANK_POWERDOWN
> > since the gpio value is literally logical low.
>
> To be honest this probably "hints" that the bootloader simply didn't
> consider the backlight at all :-) . I'd rather the patch description
> focus on what circumstances lead to the current code making a bad
> decision. More like:
>
> If the GPIO pin is in the input state but the backlight is currently
> off due to default pull downs then ...
How about this patch description?
---------------------------------8<-------------------------------------------
Without this patch, 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:
---
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.
---
So, let's drop output gpio direction check and only check gpio value to set
the initial power state.
---------------------------------8<-------------------------------------------
Regards,
Liu Ying
