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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 23 Apr 2021 14:27:05 +0200
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Subject: Re: [RFC PATCH 0/4] Support for passing runtime state idle time to TF-A
To:     Sowjanya Komatineni <skomatineni@nvidia.com>
Cc:     Sudeep Holla <sudeep.holla@arm.com>,
        Souvik Chakravarty <souvik.chakravarty@arm.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Jon Hunter <jonathanh@nvidia.com>, ksitaraman@nvidia.com,
        sanjayc@nvidia.com,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
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        Linux PM <linux-pm@vger.kernel.org>,
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On Thu, Apr 22, 2021 at 10:31 PM Sowjanya Komatineni
<skomatineni@nvidia.com> wrote:
>
> Tegra194 and Tegra186 platforms use separate MCE firmware for CPUs which is
> in charge of deciding on state transition based on target state, state idle
> time, and some other Tegra CPU core cluster states information.
>
> Current PSCI specification don't have function defined for passing runtime
> state idle time predicted by governor (based on next events and state target
> residency) to ARM trusted firmware.

Presumably that's because this is not a good idea.

A basic design principle of cpuidle is that it should be possible to
use every governor with every driver and the changes in this series
make the platforms in question only work with menu AFAICS.