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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 9:37:29 AM PDT, Ingo Molnar <> wrote:
>* <> wrote:
>> > Just to check, you mean: EFI reboot (and shutdown) become the
>> > methods when the machine is booted in EFI mode, and EFI stuff has
>> > been disabled with a kernel parameter?
>> > Even when running in full hardware ACPI mode.
>No, I still think "early" EFI is historically better with ACPI reboot.
>But can we find a firmware flag perhaps that will *not* result in EFI
>reboot being turned off?
>> This, I believe, is known to not work.
>Yeah, I bet so.
>My problem is that the code appears to have the wrong assumptions:
> /*
>* For most modern platforms the preferred method of powering off is via
> * ACPI. However, there are some that are known to require the use of
> * EFI runtime services and for which ACPI does not work at all.
> *
> * Using EFI is a last resort, to be used only if no other option
> * exists.
> */
> bool efi_reboot_required(void)
> {
> if (!acpi_gbl_reduced_hardware)
> return false;
> efi_reboot_quirk_mode = EFI_RESET_WARM;
> return true;
> }
>At minimum the comment is stale: "modern" platforms, *especially* when
>the only bootup method is EFI, as in the ACER laptop case, I think the
>preferred reboot method is absolutely an EFI reboot - and it's probably
>what Windows uses too.
>The question is, is acpi_gbl_reduced_hardware false on the Acer
>TravelMate X514-51T? I think it has to be, for the quirk to make sense
>if it's true then efi_reboot_required() would set the reboot method to
>I.e. we seem to have a new category of systems that are advertising
>themselves as 'full ACPI compliant', which are NOT old EFI systems, but
>modern EFI systems.
>Is there some good way to detect these - such as ACPI version or
> Ingo

That is exactly what the reduced hardware flag is supposed to indicate. As far as what Windows does, the are only two ways to find out: testing somehow, or these days Microsoft might actually answer if we ask nicely.
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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