linux-kernel - Re: [RFC PATCH v1 6/6] soc/tegra: regulators: Add regulators coupler for Tegra30

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Message-ID: <20190512090446.GN21483@sirena.org.uk>
Date:   Sun, 12 May 2019 18:04:46 +0900
From:   Mark Brown <broonie@...nel.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 6/6] soc/tegra: regulators: Add regulators coupler
 for Tegra30

On Wed, May 08, 2019 at 04:27:42PM +0300, Dmitry Osipenko wrote:

> Constraints:

> 1) The max-spread voltage is 300mV.

> 2) CORE voltage must be higher than the CPU by at least N mV, where N
> varies depending on the CPU voltage.

Those seem like they should be doable in generic code, though the fact
that the constraint is variable makes it annoying to specify - otherwise
it'd just be a minimum and maximum spread.  I'm not really coming up
with any great ideas right now, it's getting into OPP type territory but
it sounds like there's more flexibility for ramping the core voltage so
you'd end up with silly numbers of OPPs.

> 3) There is a constraint on the maximum CORE voltage depending on
> hardware model/revision (cpu_speedo_id) where a higher voltages
> apparently may cause physical damage, so it's better to hardcode the
> limitation in the code rather than to rely on a board's device-tree
> description. This constraint is quite vaguely defined in the downstream
> kernel, I'm not really sure if it's solely about the hardware safety.

I'd expect this to be enforced by the cpufreq driver just not selecting
higher voltages on affected parts.

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