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

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Date:   Wed, 10 Mar 2021 15:19:35 -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 3/8/21 10:32 AM, Sowjanya Komatineni wrote:
>
> 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.
>
Hi Sudeep,

Can you please let me know if you have any more concerns for having this 
Tegra specific cpuidle driver?

Thanks

Sowjanya