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

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Message-ID: <20200504164027.tvlkcbfoz3igeh6x@gilmour.lan>
Date:   Mon, 4 May 2020 18:40:27 +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

Hi,

On Thu, Apr 30, 2020 at 03:48:04PM +0200, Clément Péron wrote:
> On Tue, 28 Apr 2020 at 18:45, Maxime Ripard <maxime@...no.tech> wrote:
> >
> > 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 ?
> 
> As this could take more time than expected,
> 
> Could you drop the commit :
> add1e27fb703f65f33191ccc70dd9d811254387c
> arm64: dts: allwinner: h6: Enable CPU opp tables for Tanix TX6

It's done, thanks!
Maxime

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