linux-kernel - Re: [PATCH 1/3] dt-bindings: arm,psci: Allow S2RAM power

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Message-ID: <54cc4221-ba5f-4741-9033-20874265ca01@oss.qualcomm.com>
Date: Thu, 19 Dec 2024 20:43:27 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Sudeep Holla <sudeep.holla@....com>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Lorenzo Pieralisi
 <lpieralisi@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Bjorn Andersson <bjorn.andersson@....qualcomm.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH 1/3] dt-bindings: arm,psci: Allow S2RAM power_state
 parameter description

On 6.12.2024 11:21 AM, Sudeep Holla wrote:
> On Mon, Oct 28, 2024 at 03:22:57PM +0100, Konrad Dybcio wrote:
>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>
>> Certain firmware implementations (such as the ones found on Qualcomm
>> SoCs between roughly 2015 and 2023) expose an S3-like S2RAM state
>> through the CPU_SUSPEND call, as opposed to exposing PSCIv1.0's
>> optional PSCI_SYSTEM_SUSPEND.
>>
> 
> If so, can you elaborate why s2idle doesn't work as an alternative to what
> you are hacking up here.

Please see other branches of this thread

> 
>> This really doesn't work well with the model where we associate all
>> calls to CPU_SUSPEND with cpuidle. Allow specifying a single special
>> CPU_SUSPEND suspend parameter value that is to be treated just like
>> SYSTEM_SUSPEND from the OS's point of view.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>> ---
>>  Documentation/devicetree/bindings/arm/psci.yaml | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/arm/psci.yaml b/Documentation/devicetree/bindings/arm/psci.yaml
>> index cbb012e217ab80c1ca88e611e7acc06c6d56fad0..a6901878697c8e1ec1cbfed62298ae3bc58f2501 100644
>> --- a/Documentation/devicetree/bindings/arm/psci.yaml
>> +++ b/Documentation/devicetree/bindings/arm/psci.yaml
>> @@ -98,6 +98,12 @@ properties:
>>        [1] Kernel documentation - ARM idle states bindings
>>          Documentation/devicetree/bindings/cpu/idle-states.yaml
>>  
>> +  arm,psci-s2ram-param:
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    description:
>> +      power_state parameter denoting the S2RAM/S3-like system suspend state
> 
> Yet another NACK as this corresponds to PSCI SYSTEM_SUSPEND and as per
> specification it takes no such parameter. This is just misleading.
> 

Yeah PSCI_SYSTEM_SUSPEND takes care of this on platforms that expose it.

DEN0022F.b Section 6.5. recommends that CPU_SUSPEND StateID includes
a field for system-level power down states. This binding change only
adds a way for DT-based platforms to associate such state with S2RAM
suspend.

That may be a bit Linux-specific whereas bindings are supposed to be
OS-agnostic, but since we effectively want one PSCI state for deep
suspend regardless of the OS, I would think this kind of hint is fine.

Konrad