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

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Date:   Tue, 21 Feb 2017 11:14:16 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Pavel Machek <pavel@....cz>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        Lina Iyer <lina.iyer@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Magnus Damm <magnus.damm@...il.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC 3/6] drivers: firmware: psci: Implement shallow
 suspend mode



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
broken.

-- 
Regards,
Sudeep