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

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Date: Mon, 8 Jan 2024 16:47:05 +0100
From: Konrad Dybcio <konradybcio@...nel.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 3.01.2024 10:44, Sudeep Holla wrote:
> On Tue, Jan 02, 2024 at 07:17:50PM +0100, Konrad Dybcio wrote:
>> 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
>>
> 
> Thanks for the confirmation.
> 
>>>
>>> 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
> 
> Agreed and your PATCH 1/2 does that exactly and hence I have acked it
> already.
> 
>> all platforms with SYSTEM_SUSPEND and Qualcomm which sneaked equivalent
>> functionality into the CPU_SUSPEND call.
>>
> 
> But I don't like the Qualcomm specific changes.

Is that because of the matching table, or due to the slightly more
convoluted way of suspending the platform through CPU_SUSPEND?

If the former, I can think of other solutions. If the latter, I'm
open to keep convincing you :D There are probably things I skipped
over when explaining how it's wired up..

Konrad