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 06:57:05 +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,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>, ksitaraman@...dia.com,
        sanjayc@...dia.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 Fri, Mar 12, 2021 at 02:27:30PM -0800, Sowjanya Komatineni wrote:
> Hi Sudeep,
>
> To make our driver PSCI compliant below are few updates to be done
>
> 1. Standardize passing residency time run-time thru PSCI to ATF.
>

Yes that was my initial understanding, but your previous response was
confusing. I should have read this first.

>     From PSCI specification I only see PSCI_STAT_RESIDENCY and
> PSCI_STAT_COUNT optional functions for PSCI1.0/PSCI1.1
>

Indeed, we don't have any support to pass run-time residency hints in PSCI
today.

>    Can you please help add right people to explore on possible ways to add
> PSCI function for passing corresponding state residency time to ATF?
>

Before we jump to implementation in TF-A we need to get agreement to get this
added to the specification to support in OSPM/Linux. TF-A is just one
implementation of PSCI and may not be only one.

Formally you can raise any specification related queries to
https://developer.arm.com/support or support@....com. I will ask the author
of PSCI specification internally to take a look at this thread and chime in
if they can.

> 2. Tegra CPU Idle support definitely need to pass deepest cluster state and
> threshold to MCE firmware from DT and looks like we can move this
> implementation to ATF
>

Yes, I just asked the same question as response to your earlier email. Thanks
for confirming that it can be moved out of OSPM/Linux and DT

>      With both of the above implementation changes Tegra194 driver will be
> PSCI compliant.
>

We still need to get agreement on the specification front 😉.

--
Regards,
Sudeep