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SubjectRe: EFI reboot vs. ACPI reboot (was: Re: [tip:x86/urgent] x86/reboot, efi: Use EFI reboot for Acer TravelMate X514-51T)
On April 17, 2019 5:38:41 AM PDT, Daniel Drake <> wrote:
>On Wed, Apr 17, 2019 at 2:16 PM Ingo Molnar <> wrote:
>> Ok, so acpi_gbl_reduced_hardware is set when the ... 'reduced
>> 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
>> 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.

This, I believe, is known to not work.
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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