linux-kernel - Re: s2idle breaks on machines without cpuidle support

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Date:   Wed, 8 Feb 2023 15:03:06 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Kazuki <kazukih0205@...il.com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>
Subject: Re: s2idle breaks on machines without cpuidle support

On Wed, Feb 08, 2023 at 11:43:27PM +0900, Kazuki wrote:
> On Wed, Feb 08, 2023 at 02:16:58PM +0000, Sudeep Holla wrote:

[...]

> > I was about ask you earlier as why can't you implement just system
> > suspend in PSCI where the last cpu just calls WFI if you are interested
> > in system sleep state. Or you can implement CPU_SUSPEND with an additional
> > retention state which enters PSCI implementation just to make sure there is
> > an active cpuidle driver and the s2idle state machinery works as expected.
>
> The machine I have (Macbook with Apple M1) doesn't have PSCI.

Well, if we are allowing to boot on such a system, then we must allow
adding a platform specific idle driver. It may be useful once we info
to add deeper than WFI states.

> I guess we should ensure that systems without a cpuidle driver
> will not suspend maybe around here then.
>

Are we ? I thought were making changes to enable it. Or are you saying
we allow to enter into such a state and render the system unusable, if
so we need to fix it.

--
Regards,
Sudeep