linux-kernel - Re: [PATCH 2/2] firmware/psci: Set pm_set_resume/suspend_via

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Date: Tue, 2 Jan 2024 19:17:50 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Sudeep Holla <sudeep.holla@....com>
Cc: Mark Rutland <mark.rutland@....com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Marijn Suijten <marijn.suijten@...ainline.org>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Bjorn Andersson <andersson@...nel.org>
Subject: Re: [PATCH 2/2] firmware/psci: Set
 pm_set_resume/suspend_via_firmware() on qcom

On 28.12.2023 13:43, Sudeep Holla wrote:
> On Thu, Dec 28, 2023 at 01:16:28PM +0100, Konrad Dybcio wrote:
>> On 28.12.2023 12:50, Sudeep Holla wrote:
>>> On Thu, Dec 28, 2023 at 12:47:51PM +0100, Konrad Dybcio wrote:
>>>> On 28.12.2023 11:28, Sudeep Holla wrote:
>>>>> On Wed, Dec 27, 2023 at 11:15:31PM +0100, Konrad Dybcio wrote:
>>>>>> Most Qualcomm platforms implementing PSCI (ab)use CPU_SUSPEND for
>>>>>> entering various stages of suspend, across the SoC. These range from a
>>>>>> simple WFI to a full-fledged power collapse of the entire chip
>>>>>> (mostly, anyway).
>>>>>>
>>>>>> Some device drivers are curious to know whether "the firmware" (which is
>>>>>> often assumed to be ACPI) takes care of suspending or resuming the
>>>>>> platform. Set the flag that reports this behavior on the aforementioned
>>>>>> chips.
>>>>>>
>>>>>> Some newer Qualcomm chips ship with firmware that actually advertises
>>>>>> PSCI SYSTEM_SUSPEND, so the compatible list should only grow slightly.
>>>>>>
>>>>>
>>>>> NACK, just use suspend-to-idle if SYSTEM_SUSPEND is not advertised. It is
>>>>> designed for such platforms especially on x86/ACPI which don't advertise
>>>>> Sx states. I see no reason why that doesn't work on ARM platforms as well.
>>>>
>>>> Not sure if I got the message through well, but the bottom line is, on
>>>> Qualcomm platforms the "idle" states aren't actually just "idle" (read:
>>>> they're not like S0ix). All but the most shallow ones shut down quite a
>>>> chunk of the entire SoC, with the lowest ones being essentially S3 with
>>>> power being cut off from the entire chip, except for the memory rail.
>>>>
>>>
>>> No I understood that and S2I is exactly what you need.
>>> Have you checked if S2I already works as intended on these platforms ?
>> Yes, simple CPU idling works OOTB and the SoC power collapse only works
>> given the developer doesn't cut corners when bringing up the platform
>> (read: works on some of the ones we support, trying hard to expand that
>> group!)
>>
>>> What extra do you achieve with this hack by advertising fake S2R ?
>> Uh.. unless I misunderstood something, I'm not advertising s2ram..
>> Quite the opposite, I'm making sure only s2idle is allowed.
>>
> 
> Right, I didn't notice that in suspend_valid_all(), it can be rename
> suspend_valid_s2i or something. "All" indicates all state is valid.
> 
> Anyways that is not the main point. IIUC S2I must still work if there is
> at-least one CPU idle state other than WFI without these changes. Right ?

Yes, and it does

> 
> If all these changes is to support S2I wih WFI only, then we can look at
> some generic solution as there were previous attempts to do something
> similar on other platforms IIRC.

No, I'm just interested in setting the resume/suspend_via_firmware()
markers and the PSCI driver seems like a good place for it, be it on
all platforms with SYSTEM_SUSPEND and Qualcomm which sneaked equivalent
functionality into the CPU_SUSPEND call.

Konrad