Re: [PATCH/RFC 3/6] drivers: firmware: psci: Implement shallow suspend mode

From: Sudeep Holla
Date: Tue Feb 21 2017 - 06:14:39 EST

On 21/02/17 11:07, Pavel Machek wrote:
> Hi!
>> Enable support for "shallow" suspend mode, also known as "Standby" or
>> "Power-On Suspend".
>> As secondary CPU cores are taken offline, "shallow" suspend mode saves
>> slightly more power than "s2idle", but less than "deep" suspend mode.
>> However, unlike "deep" suspend mode, "shallow" suspend mode can be used
>> regardless of the presence of support for PSCI_SYSTEM_SUSPEND, which is
>> an optional API in PSCI v1.0.
> If system supports "shallow" suspend, why does not PSCI implement it?

Yes it can, and IIUC it already does on this platform with CPU_SUSPEND.
All it now needs is just to use existing "freeze" suspend mode in Linux.

> In the past, I was told PSCI will not turn into ACPI-like mess, and
> that we'll be able to fix PSCI and will not have to work around its
> problems in kernel :-(.

Can you be more elaborate on the mess you see on this Renesas platform.

For me, it looks like this patch is attempting to *re-implement* the
existing "suspend-to-idle" functionality. So IMO, this patch set is
creating unnecessary mess giving an illusion that PSCI specification is