Messages in this thread | | | From | Daniel Drake <> | Date | Wed, 17 Apr 2019 20:38:41 +0800 | Subject | Re: EFI reboot vs. ACPI reboot (was: Re: [tip:x86/urgent] x86/reboot, efi: Use EFI reboot for Acer TravelMate X514-51T) |
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On Wed, Apr 17, 2019 at 2:16 PM Ingo Molnar <mingo@kernel.org> wrote: > Ok, so acpi_gbl_reduced_hardware is set when the ... 'reduced hardware' > bit is set: > > acpi_gbl_reduced_hardware = FALSE; > if (acpi_gbl_FADT.flags & ACPI_FADT_HW_REDUCED) { > acpi_gbl_reduced_hardware = TRUE; > } > > > which is described as: > > #define ACPI_FADT_HW_REDUCED (1<<20) /* 20: [V5] ACPI hardware is not implemented (ACPI 5.0) */ > > That seems counter-intuitive to me: if no full ACPI hardware is > implemented then we should assume reduced ACPI functionality, i.e. if the > EFI runtime is otherwise available we should default to it.
It's a bit confusing, but my loose understanding is that previous versions of the ACPI spec required system implementors to implement the whole thing; but that's increasingly impractical today, e.g. with ARM systems coming along, which do not gel well with some of the historical x86-rooted design aspects that spilled over into ACPI. The V5 spec introduces reduced mode as an opt-in new feature, but for compatibility with pre-V5 implementations it needs to consider "full hardware" mode as the default.
> Feel free to send a patch that makes EFI reboot the default one under > these circumstances,
Just to check, you mean: EFI reboot (and shutdown) become the default methods when the machine is booted in EFI mode, and EFI stuff has not been disabled with a kernel parameter? Even when running in full hardware ACPI mode.
Thanks Daniel
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