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

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Message-ID: <Z2VUiHWHgbWowdal@bogus>
Date: Fri, 20 Dec 2024 11:27:04 +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>,
	Sudeep Holla <sudeep.holla@....com>,
	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 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.

> 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.
>

Sure, just use the CPU_SUSPEND bindings that already exist. No need to
define this as some special case if it is exposed as CPU_SUSPEND idle
state. Not sure why you want to do it differently. I understand the
need to handle it different in the kernel, but I don't understand to
define the new bindings for that. Just use the existing bindings for the
idle states. Again I see no exception for this case.

> 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.
>

Exactly, that's the reason for not changing this into special case and
special binding for that special case created.

--
Regards,
Sudeep