acpi: Forbid requesting S4 when S4BIOS is not supported
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Authored by olce on Jun 3 2026, 4:54 PM.

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obiwac

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rGfc6d7a7520d0: acpi: Forbid requesting S4 when S4BIOS is not supported

Summary

Pending the OS-supported hibernate functionality, prevent requesting S4
when S4BIOS is not supported.

To this end, make sure that acpi_supported_stypes[] indicates that
POWER_STYPE_FW_HIBERNATE is not supported if 'acpi_s4bios_supported' is
false, even if S4 is supported by the platform (which is only
a power-down-like state, without any support to save the system image by
itself). This will cause requests to enter S4, which are translated to
POWER_STYPE_FW_HIBERNATE before reaching
acpi_ReqSleepState()/acpi_EnterSleepState(), to fail in this case.

Retire the 'hw.acpi.s4bios' sysctl knob, as having it to 0 by default
(S4BIOS not supported) or setting it to 0 (default is 1 when S4BIOS is
supported) could only lead, on a S4 request, to a power down without any
possibility to restore the system (and, since a recent commit, it has
not been possible anymore to force it to 1 when S4BIOS is not announced
supported in the FACS table, which would cause a failure or a crash).

When OS-supported hibernate is introduced, it will become the default
hibernate method over S4BIOS, as we have not heard of any semi-recent
hardware platform implementing it (and when it is, it usually needs
a sufficiently large dedicated slice/partition, and does not use FreeBSD
swap slices/partitions). Then, for people still wanting to use S4BIOS
on older platforms that support it, the tentative plans are to modify
acpiconf(8) to accept '4BIOS' as an argument to '-s', or modify zzz(8)
so that one can pass a specific suspension method.

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rG FreeBSD src repository

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Build Status

Buildable 73668
Build 70551: arc lint + arc unit

Event Timeline

olce created this revision.Jun 3 2026, 4:54 PM

Herald added a subscriber: imp. · View Herald TranscriptJun 3 2026, 4:54 PM

olce requested review of this revision.Jun 3 2026, 4:54 PM

Harbormaster completed remote builds in B73642: Diff 179142.Jun 3 2026, 4:54 PM

olce added a parent revision: D57413: acpi: Move supported states arrays into the softc.Jun 3 2026, 4:54 PM

Remove remaining declaration for acpi_s4bios_sysctl() in acpi.c
Add a comment in the acpi_sleep_machdep() functions explaining why we are just testing on S4 state before calling AcpiEnterSleepStateS4bios().

Harbormaster completed remote builds in B73668: Diff 179199.Jun 4 2026, 11:45 AM

my only concern with making S4 BIOS its own ACPI sleep state is that we won't really have a way of making the fw_hibernate sleep type map to it, and we might have to re-add a similar sysctl to s4bios

sys/dev/acpica/acpi.c
648–653	maybe update this comment to mention this is only until we have S4 non-bios support

olce marked an inline comment as done.Sat, Jun 20, 7:27 PM

olce added inline comments.

sys/dev/acpica/acpi.c
648–653	This is intended to stay as is. Actually, OS-initiated hibernate will be requested through `POWER_STYPE_OS_HIBERNATE` (which I have in some commit somewhere, for a later revision). As said above in the commit message, people using `acpiconf -s 4` will get OS-initiated hibernate when it's released, and no more S4BIOS, which will have to be requested through `acpiconf -s 4bios` or `zzz --something`. Let's talk about it directly if that isn't clear (or if there's still a problem with or in this frame).