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

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Date:   Tue, 21 Feb 2017 17:23:48 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        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>, Pavel Machek <pavel@....cz>,
        Rob Herring <robh+dt@...nel.org>,
        Magnus Damm <magnus.damm@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC 3/6] drivers: firmware: psci: Implement shallow
 suspend mode

Hi Sudeep,

On Tue, Feb 21, 2017 at 11:42 AM, Sudeep Holla <sudeep.holla@....com> wrote:
> On 20/02/17 20:33, Geert Uytterhoeven wrote:
>> 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.
>>
>> List the available system suspend modes:
>>
>>     $ cat /sys/power/mem_sleep
>>     s2idle shallow [deep]
>>
>> Suspend to "shallow" mode:
>>
>>     $ echo shallow > /sys/power/mem_sleep
>>     $ echo mem > /sys/power/state
>>
>
> I don't have the links to such previous attempts handy, but we have

Don't worry, I did read earlier discussions about implementing shallow mode.

> more elegant alternative options(suspend-to-idle) and any such attempts
> to hack around the PSCI will be NACKed.

"s2idle" does not power down secondary CPU cores, so this is an improvement.
"deep" may not support configured wake-up sources, which is a bug.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds