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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Date:	Mon,  3 Aug 2015 10:37:51 +0200 (CEST)
From:	"Timo Sigurdsson" <public_timo.s@...entcreek.de>
To:	julian.calaby@...il.com
Cc:	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, maxime.ripard@...e-electrons.com,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
	wens@...e.org
Subject: Re: [linux-sunxi] [PATCH] ARM: dts: sunxi: Raise minimum CPU voltage for sun7i-a20 to a level all boards can supply

Hi Julian,

Julian Calaby schrieb am 03.08.2015 01:35:
>> sun7i-a20.dtsi contains an cpufreq operating point at 0.9 volts. Most A20
>> boards
>> (or all?), however, do not allow the voltage to go below 1.0V. Thus, raise the
>> voltage for the lowest operating point to 1.0V so all boards can actually use
>> it.
> 
> Surely it wouldn't be added here if some could supply 0.9v.

Maybe. I just know some boards don't (e.g. Cubieboard 2, Cubietruck, BananaPi)
and don't know of any that does. But that's not my point. I think that a common
minimum operating point, defined on the SOC level, should be defined in a way
that works on all boards.

> 
> Is the code that uses this smart enough to sensibly switch between two
> operating points with the same frequency and different voltages? If
> so, maybe just add a 144MHz @ 1.0v operating point?

I never tried and I probably won't have time to test that before the weekend.
The current behaviour is this, though: On boards that set their minimum CPU
voltage to 1.0V, the lowest operating point will simply not be available to
the user.

> (Alternatively, would it make sense to modify the code that uses this
> to use frequencies with voltages specified that are lower than can be
> supplied with the lowest voltage it can?)

Considering OPPv2 is in the works, maybe not?


Thanks,

Timo
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