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

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Message-ID: <c80c4cdb-48e1-4b6f-8ab8-fad6e100af00@oss.qualcomm.com>
Date: Fri, 20 Dec 2024 14:57:34 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Sudeep Holla <sudeep.holla@....com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>, 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>
Subject: Re: [PATCH 1/3] dt-bindings: arm,psci: Allow S2RAM power_state
 parameter description

On 20.12.2024 2:55 PM, Sudeep Holla wrote:
> On Fri, Dec 20, 2024 at 01:54:45PM +0100, Konrad Dybcio wrote:
>> On 20.12.2024 12:27 PM, Sudeep Holla wrote:
>>> On Thu, Dec 19, 2024 at 08:43:27PM +0100, Konrad Dybcio wrote:
>>>> 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.
>>>>
>>>
>>> And those that don't advertise/expose don't get to use, simple.
>>
>> The spec says:
>>
>> "The call is equivalent to using the CPU_SUSPEND call for the
>> deepest possible platform powerdown state."
>>
> 
> Please take a look at the preconditions for both the calls. They are
> different.

Which is *precisely* why I want to tell the OS that it's a S2RAM state,
so that different actions can be taken in peripheral device drivers.

Konrad