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

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Message-ID: <4cebf482-a2f8-5a79-a2f6-4ccd7d31c6ad@nvidia.com>
Date:   Mon, 8 Mar 2021 10:32:17 -0800
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <daniel.lezcano@...aro.org>, <robh+dt@...nel.org>,
        <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 3/7/21 8:37 PM, Sudeep Holla wrote:
> On Wed, Mar 03, 2021 at 10:08:10PM -0800, Sowjanya Komatineni wrote:
>> This patch adds cpu-idle-states and corresponding state nodes to
>> Tegra194 CPU in dt-binding document
>>
> I see that this platform has PSCI support. Can you care to explain why
> you need additional DT bindings and driver for PSCI based CPU suspend.
> Until the reasons are convincing, consider NACK from my side for this
> driver and DT bindings. You should be really using those bindings and
> the driver may be with minor changes there.
>
MCE firmware is in charge of state transition for Tegra194 carmel CPUs.

For run-time state transitions, need to provide state request along with 
its residency time to MCE firmware which is running in the background.

State min residency is updated into power_state value along with state 
id that is passed to psci_cpu_suspend_enter

Also states cross-over idle times need to be provided to MCE firmware.

MCE firmware decides on state transition based on these inputs along 
with its background work load.

So, Tegra specific CPU idle driver is required mainly to provide 
cross-over thresholds from DT and run time idle state information to MCE 
firmware through Tegra MCE communication APIs.

Allowing cross-over threshold through DT allows users to vary idle time 
thresholds for state transitions based on different use-cases.