linux-kernel - Re: [PATCH v1 3/5] dt-bindings: arm: Add cpu-idle-states to Tegra194 CPU nodes

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Date:   Tue, 16 Mar 2021 07:18:11 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com,
        daniel.lezcano@...aro.org, robh+dt@...nel.org,
        ksitaraman@...dia.com, sanjayc@...dia.com,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Sudeep Holla <Sudeep.Holla@....com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v1 3/5] dt-bindings: arm: Add cpu-idle-states to Tegra194
 CPU nodes

On Mon, Mar 15, 2021 at 11:13:24AM -0700, Sowjanya Komatineni wrote:
> Hi Sudeep,
>
> I see you are one of the maintainer of PSCI driver. Please add any other
> right persons if you think should also agree/comment.
>
> Can you please comment on below 2 items based on your feedback?
>
> 1. Can you please suggest on proper way of generalizing to pass state
> residency time run-time along with state during state enter?
>
> Not sure if any other drivers need this but for Tegra as MCE firmware is
> in-charge of states enter and decisions, passing run-time state residency
> from kernel to ATF is required and agree on not using power_state value for
> this which is against PSCI spec.
>

Yes, I prefer you need to get this added in the PSCI specification.
I have passed this thread to the author of the specification.

> 2. Regarding state thresholds, although state thresholds are policy related
> in Tegra cpu idle perspective these thresholds are platform specific based
> on use case and mainly for MCE firmware usage to decide on state transitions
> for core and core clusters as well.
>
>From previous emails, I gather these can be moved to firmware and need not be
there in DT ?

> As these are Tegra platform specific, Please comment if any other concerns
> in having this configured by Tegra CPU Idle kernel driver.
>

I prefer not to have Tegra specific idle driver if we can get the necessary
changes in PSCI spec. We must then have just one PSCI idle driver in the
kernel.


> Based on my understanding only above issue-1 is PSCI compliant related.
> Please confirm.
>

Correct.

--
Regards,
Sudeep