linux-kernel - 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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Message-ID: <CAKv+Gu9NJH02obRtgtNf7O7Bd8Z0SdKjsBLppGd60f6ryq6OoA@mail.gmail.com>
Date:   Wed, 17 Apr 2019 12:07:50 -0700
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Daniel Drake <drake@...lessm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jian-Hong Pan <jian-hong@...lessm.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        linux-efi <linux-efi@...r.kernel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>,
        Endless Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: EFI reboot vs. ACPI reboot (was: Re: [tip:x86/urgent] x86/reboot,
 efi: Use EFI reboot for Acer TravelMate X514-51T)

On Wed, 17 Apr 2019 at 11:23, Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Prakhya, Sai Praneeth <sai.praneeth.prakhya@...el.com> wrote:
>
> > I will ask around internally to check if it is a good idea to make EFI
> > reboot the default method when the machine is booted in EFI mode.
>
> Or whether there's some robust signature that indicates "modern EFI
> system where EFI reboot is the primary method"?
>
> Major EFI version or ACPI version or such?
>

I am actually at Microsoft right now, and I managed to get
clarification on how Windows deals with this: Windows will attempt to
use ACPI reboot first, and will only attempt to use anything else if
that fails. EFI reset is actually its least preferred option, and so
it is highly likely that it is untested on most of the shipping x86
hardware if any of the other methods work.

So let's not touch this.