On Sun, Jul 17, 2022 at 8:14 AM Zhang Rui <rui.zhang@xxxxxxxxx> wrote: > > On Thu, 2022-07-14 at 21:11 +0200, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > > > > If ACPI_FADT_LOW_POWER_S0 is not set, this doesn't mean that low- > > power > > S0 idle is not usable. It merely means that using S3 on the given > > system is more beneficial from the energy saving perspective than > > using > > low-power S0 idle, as long as S3 is supported. > > Agreed. > > > > > Suspend-to-idle is still a valid suspend mode if > > ACPI_FADT_LOW_POWER_S0 > > is not set and the pm_suspend_via_firmware() check in > > pch_wpt_suspend() > > is sufficient to distinguish suspend-to-idle from S3, so drop the > > confusing ACPI_FADT_LOW_POWER_S0 check. > > the cooling delay in the suspend callback is to make sure PCH > temperature won't block S0ix during s2idle. So if S0ix is not > supported, it is meaningless to invoke the cooling delay during s2idle. But there is no way to determine whether or not S0ix is supported. In particular, ACPI_FADT_LOW_POWER_S0 is not one. > so the problem is that we don't have an indicator for S0ix capability. > And this also applies to drivers/rtc/rtc-cmos.c, where we use ACPI SCI > for runtime RTC wakeup instead of HPET interrupt on "S0ix capable" > platforms because the HPET timer may block S0ix. "S0ix capable" doesn't matter. What matters is whether or not the current transition under way is into S0 or into suspend-to-idle. In the latter case there is no reason to avoid doing whatever is done in the expectation that S0ix may be entered going forward.
