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 11:16:24 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Julian Calaby <julian.calaby@...il.com>
Cc:	public_timo.s@...entcreek.de, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	devicetree <devicetree@...r.kernel.org>,
	"Mailing List, Arm" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Chen-Yu Tsai <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

On Mon, Aug 03, 2015 at 09:35:51AM +1000, Julian Calaby wrote:
> Hi Timo,
> 
> On Mon, Aug 3, 2015 at 5:23 AM, Timo Sigurdsson
> <public_timo.s@...entcreek.de> wrote:
> > 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.
> 
> 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?

And how would it choose between the two exactly ? Switch to the 144MHz
@ 0.9V and see if it works ? If it doesn't you might have screwed your
system already, and might not be able to recover from it at all.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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