linux-kernel - Re: [PATCH 0/3] Allow specifying an S2RAM sleep on pre-SYSTEM

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Message-ID: <db755bda-8464-4882-a72b-1d860abcb2fe@oss.qualcomm.com>
Date: Fri, 20 Dec 2024 15:57:48 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Sudeep Holla <sudeep.holla@....com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Elliot Berman <quic_eberman@...cinc.com>,
        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 0/3] Allow specifying an S2RAM sleep on pre-SYSTEM_SUSPEND
 PSCI impls

On 20.12.2024 3:36 PM, Sudeep Holla wrote:
> On Fri, Dec 20, 2024 at 03:20:37PM +0100, Konrad Dybcio wrote:
>>
>> I would happen to think that, yes. Especially since the reference firmware
>> implementation does *exactly this*:
>>
>> https://github.com/ARM-software/arm-trusted-firmware/blob/master/lib/psci/psci_main.c#L179-L221
>>
>> PSCI_SYSTEM_SUSPEND seems to be simply meant as a wrapper around a specific
>> CPU_SUSPEND state (which may or may not be only callable from inside the
>> firmware when SYSTEM_SUSPEND specifically is requested, for reasons),
>> in a platform-agnostic way, so that the OS can enter suspend without
>> providing that magic StateID on all supported platforms.
> 
> Exactly, that's how it can be OS and platform agnostic. Yet this platform
> considered to optimise by not just providing it as a wrapper(if it was
> that simple on your platform too) without running any tests and leaving
> it to interested parties like you to mess around to get it working.
> That practice needs to be fixed and this change won't help and once we
> fix this, more such special treatment fixes are needed on newer platforms.
> So lets stop and ensure things are fixed properly.

And then remove CPU_SUSPEND support if CPU_SUSPEND2 comes in a spec update
because it's not generic enough? Sorry, this is not acceptable.

If you enforce PSCI as the only way of doing SMP/cpuidle/platform suspend
upstream on arm64, you should not gatekeep existing implementations that are
actually in line with the written spec, just because you don't happen to
like them.

If you want to start the process of getting rid of those, amend the spec
to deprecate and/or forbid system-level suspend in CPU_SUSPEND in future
PSCI versions. But you can't retroactively change your decisions like that.

>> But since it already requires more elbow grease on the peripheral IP side,
>> I'm not really convinced it's that much useful.
>>
>> Plus, the optional bit of doing more work behind the scenes doesn't seem
>> to be very wildly used across TF-A supported platforms.
>>
>> So please, stop making the argument that it's any different. The firmware
>> I'm dealing with simply didn't expose the same thing twice, in perfect
>> accordance with the spec.
>>
> 
> So that it can continue to do so in the future ?
> Thanks but no thanks. NACK with no arguments as requested.

That's already been "fixed" on QC platforms starting around 2022, as
mentioned in this series.

Konrad