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

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Date: Thu, 28 Dec 2023 12:47:51 +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 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.

Konrad