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

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Message-ID: <Z2V3amqWYDUWA2uM@bogus>
Date: Fri, 20 Dec 2024 13:55:54 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: 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 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.

--
Regards,
Sudeep