linux-kernel - Re: [linux-sunxi] Re: [PATCH v2] arm64: dts: allwinner: h6: Use dummy regulator for Tanix TX6

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Date:   Tue, 28 Apr 2020 18:45:22 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Clément Péron <peron.clem@...il.com>
Cc:     Robin Murphy <robin.murphy@....com>, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Piotr Oniszczuk <warpme@...pl>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [linux-sunxi] Re: [PATCH v2] arm64: dts: allwinner: h6: Use
 dummy regulator for Tanix TX6

On Tue, Apr 28, 2020 at 06:23:35PM +0200, Clément Péron wrote:
> Hi Robin,
> 
> On Tue, 28 Apr 2020 at 17:21, Robin Murphy <robin.murphy@....com> wrote:
> >
> > On 2020-04-28 3:26 pm, Clément Péron wrote:
> > > Tanix TX6 has a fixed regulator. As DVFS is instructed to change
> > > voltage to meet OPP table, the DVFS is not working as expected.
> >
> > Hmm, isn't that really a bug in the DVFS code? I guess it's just blindly
> > propagating -EINVAL from the fixed regulators not implementing
> > set_voltage, but AFAICS it has no real excuse not to be cleverer and
> > still allow switching frequency as long as the voltage *is* high enough
> > for the given OPP. I wonder how well it works if the regulator is
> > programmable but shared with other consumers... that case probably can't
> > be hacked around in DT.
> 
> Like you, I thought that the DVFS was clever enough to understand this
> but guess not..
> 
> Maybe they are some cases where you don't want to leave the voltage high and
> reduce the frequency. But I don't know such case.

I assume the intent was to prevent a regulator driver to overshoot and end up
over-volting the CPU which would be pretty bad.

I guess we could check that the voltage is in the range opp < actual voltage <
max opp voltage ?

Maxime

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