linux-kernel - Re: [linux-sunxi] [PATCH] ARM: dts: sunxi: Raise minimum CPU voltage for sun7i-a20 to a level all boards can supply

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Message-Id: <20150804085130.602FA6C83EF9@dd34104.kasserver.com>
Date:	Tue,  4 Aug 2015 10:51:30 +0200 (CEST)
From:	"Timo Sigurdsson" <public_timo.s@...entcreek.de>
To:	maxime.ripard@...e-electrons.com
Cc:	wens@...e.org, julian.calaby@...il.com, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-sunxi@...glegroups.com, monnier@....umontreal.ca
Subject: Re: [linux-sunxi] [PATCH] ARM: dts: sunxi: Raise minimum CPU voltage for sun7i-a20 to a level all boards can supply

Hi Maxime,

Maxime Ripard schrieb am 03.08.2015 11:34:

> On Mon, Aug 03, 2015 at 11:03:52AM +0200, Timo Sigurdsson wrote:
>> Julian Calaby schrieb am 03.08.2015 06:22:
>> > My only real objection here is are there boards that can go down to
>> > 0.9v and if so, won't this change make them less power efficient in
>> > the almost-idle case? And are those power savings enough to justify
>> > not accepting this patch?
>> 
>> It will probably make those boards less power efficient, yes. On the
>> other hand, boards that have their CPU regulator set to min. 1.0V might
>> also draw more power because the lowest frequency is not available, 
>> even though the savings due to frequency are likely to be lower than
>> the savings due to voltage.
> 
> Guys, isn't this whole discussion a bit moot? We're not doing any kind
> of power management but cpufreq, so maybe there's a lot more to do
> before we actually can have these kind of arguments?
> 
> Plus this OPP has never been used anyway, so this patch is not going
> to increase the power consumption either.

You are right. When I wrote that, I was under the impression that the
Olinuxino Lime 2 board at least used this setting since it has has a cpu
regulator defined to go as low as 0.7V. But now I checked again and see
the regulator is not referenced in the cpu node, so I guess cpufreq
doesn't use it. So, this discussion was really hypothetical and more
importantly, as you mentioned, it's an out-of-spec opp that shouldn't
be supported anyway.

Thanks,

Timo
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