linux-kernel - Re: [PATCH 0/4] Broadcom STB PM PSCI extensions

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Date:   Thu, 3 Feb 2022 11:14:35 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Mark Rutland <mark.rutland@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] Broadcom STB PM PSCI extensions

On Fri, Jan 21, 2022 at 07:54:17PM -0800, Florian Fainelli wrote:
> Hi all,
> 
> This patch series contains the Broadcom STB PSCI extensions which adds
> some additional functions on top of the existing standard PSCI interface
> which is the reason for having the driver implement a custom
> suspend_ops.
> 
> These platforms have traditionally supported a mode that is akin to
> ACPI's S2 with the CPU in WFI and all of the chip being clock gated
> which is entered with "echo standby > /sys/power/state". Additional a
> true suspend to DRAM as defined in ACPI by S3 is implemented with "echo
> mem > /sys/power/state".

How different is the above "standby" state compare to the standard "idle"
(a.k.a suspend-to-idle which is different from system-to-ram/S3) ?
Suspend to idle takes all the CPUs to lowest possible power state instead
of cpu-hotplug in S2R. Also I assume some userspace has to identify when
to enter "standby" vs "mem" right ? I am trying to see how addition of
"idle" changes that(if it does). Sorry for too many questions.

-- 
Regards,
Sudeep