From: Andreas Kemnade <andreas@kemnade.info>
To: Daniel Thompson <daniel.thompson@linaro.org>
Cc: lee.jones@linaro.org, jingoohan1@gmail.com,
jacek.anaszewski@gmail.com, pavel@ucw.cz, dmurphy@ti.com,
robh+dt@kernel.org, mark.rutland@arm.com,
b.zolnierkie@samsung.com, dri-devel@lists.freedesktop.org,
linux-leds@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-fbdev@vger.kernel.org,
"H. Nikolaus Schaller" <hns@goldelico.com>
Subject: Re: [PATCH 1/2] backlight: lm3630a: add an enable gpio for the HWEN pin
Date: Tue, 10 Sep 2019 21:06:48 +0200 [thread overview]
Message-ID: <20190910210648.3594912d@kemnade.info> (raw)
In-Reply-To: <20190910102156.vmprsjebmlphkv34@holly.lan>
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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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next prev parent reply other threads:[~2019-09-10 19:07 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-08 20:37 [PATCH 0/2] backlight_lm3630a: add enable_gpios property Andreas Kemnade
2019-09-08 20:37 ` [PATCH 1/2] backlight: lm3630a: add an enable gpio for the HWEN pin Andreas Kemnade
2019-09-09 10:57 ` Daniel Thompson
2019-09-09 20:13 ` Andreas Kemnade
2019-09-10 10:21 ` Daniel Thompson
2019-09-10 19:06 ` Andreas Kemnade [this message]
2019-09-15 16:52 ` Pavel Machek
2019-09-15 17:34 ` Andreas Kemnade
2019-09-08 20:37 ` [PATCH 2/2] dt-bindings: backlight: lm3630a: add enable_gpios Andreas Kemnade
2019-09-09 10:59 ` Daniel Thompson
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