Re: [PATCH 1/2] backlight: lm3630a: add an enable gpio for the HWEN pin

Andreas Kemnade
2019-09-10T19:07:29Z

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On Tue, 10 Sep 2019 11:21:56 +0100
Daniel Thompson <daniel.thompson@linaro.org> wrote:

[...]
> > > Is this needed?
> > >
> > > This is a remove path, not a power management path, and we have no idea
> > > what the original status of the pin was anyway?
> > >
> >
> > Looking at Ishdn on page 5 of the datasheet, switching it off everytime
> > possible seems not needed. We would need to call chip_init() everytime
> > we enable the gpio or live with default values.
> > Therefore I did decide to not put it into any power management path.
> > But switching it on and not switching it off feels so unbalanced.
>
> Either the power consumed by the controller when strings aren't lit up
> matters, in which case the driver should implement proper power
> management or it doesn't matter and changing the pin state isn't needed.
>
> I'm happy with either of the above but this looks like a third way,
> where eager users could hack in a bit of extra power management by
> forcing drivers to unbind.
>
I think I will take the simple way. I am quite sure that the power
consumption with HWEN on and leds off does not matter. If someone
later comes up and finds out that I misread the datasheet, things
are prepared to be improved.
At least the hardware can be properly described in the devicetree.

Regards,
Andreas

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