acpi: New R/O 'hw.acpi.s4bios_supported' sysctl, gate S4BIOS with it
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Authored by olce on Fri, Jan 9, 5:09 PM.

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obiwac
jhb

Summary

This new sysctl knob indicates whether the ACPI implementation supports
S4BIOS (FACS present with bit S4BIOS_F set, as per the standard).

If S4BIOS is not supported, do not allow 'hw.acpi.s4bios' to be set to
true.

This is also in preparation of probably switching the default for
'hw.acpi.s4bios' to false once OSPM-initiated S4 support is ready, in
which case administrators need some way to determine whether
firmware-initiated S4 support is possible. For now, we keep the default
of setting 'hw.acpi.s4bios' to true (1) when S4BIOS is supported.

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rG FreeBSD src repository

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Build Status

Buildable 70185
Build 67068: arc lint + arc unit

Event Timeline

olce created this revision.Fri, Jan 9, 5:09 PM

Herald added a subscriber: imp. · View Herald TranscriptFri, Jan 9, 5:09 PM

olce requested review of this revision.Fri, Jan 9, 5:09 PM

Harbormaster completed remote builds in B69770: Diff 169409.Fri, Jan 9, 5:10 PM

olce added a parent revision: D54626: acpi: 'hw.acpi.s4bios' sysctl: Change type to bool, expand description.Fri, Jan 9, 5:10 PM

olce added a subscriber: emaste.Fri, Jan 9, 5:13 PM

Should we even allow hw.acpi.s4bios to be set if not supported? feels like it could be confusing to users not super familiar with power management that hw.acpi.s4bios is set but the system is not entering S4BIOS.

sys/dev/acpica/acpivar.h
533	nitpick, but i think `acpi_should_do_s4bios` or something is a clearer name that `acpi_S4_should_firmware_initiate`

Prevent users to set hw.acpi.s4bios to true if S4BIOS is not supported.

Generally, it wouldn't be prudent for backwards-compatibility to forbid a value that was accepted before. But I think it's fine to do in this case, because we always set hw.acpi.s4bios to 1 when S4BIOS is supported, and anyway we did not support OSPM-initiated S4. So, basically, no one should be trying to set hw.acpi.s4bios to true if it wasn't true by default (which means S4BIOS is supported), and if they did, that would probably just cause a crash or some malfunction but not a suspend, so keeping such a tuning was pointless, and continuing to allow it would be silly. We might want to have an extra debug knob if we ever want to force trying S4BIOS even if not reported.

Harbormaster completed remote builds in B70185: Diff 170640.Wed, Jan 28, 1:07 PM