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Date:   Wed, 17 Apr 2019 09:51:47 -0700
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Subject: Re: EFI reboot vs. ACPI reboot (was: Re: [tip:x86/urgent] x86/reboot, efi: Use EFI reboot for Acer TravelMate X514-51T)
To:     Ingo Molnar <mingo@kernel.org>
CC:     Daniel Drake <drake@endlessm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jian-Hong Pan <jian-hong@endlessm.com>,
        matt@codeblueprint.co.uk,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-efi@vger.kernel.org, Len Brown <len.brown@intel.com>,
        linux-tip-commits@vger.kernel.org,
        Endless Linux Upstreaming Team <linux@endlessm.com>
From:   hpa@zytor.com
Message-ID: <1DE9F317-8B95-40F4-89AF-A3573B1C4881@zytor.com>
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On April 17, 2019 9:37:29 AM PDT, Ingo Molnar <mingo@kernel=2Eorg> wrote:
>
>* hpa@zytor=2Ecom <hpa@zytor=2Ecom> wrote:
>
>> > 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=2E
>
>No, I still think "early" EFI is historically better with ACPI reboot=2E
>
>But can we find a firmware flag perhaps that will *not* result in EFI=20
>reboot being turned off?
>
>> This, I believe, is known to not work=2E
>
>Yeah, I bet so=2E
>
>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=2E However, there are some that are known to require the use of
>  * EFI runtime services and for which ACPI does not work at all=2E
>  *
>  * Using EFI is a last resort, to be used only if no other option
>  * exists=2E
>  */
> bool efi_reboot_required(void)
> {
>         if (!acpi_gbl_reduced_hardware)
>                 return false;
>
>         efi_reboot_quirk_mode =3D EFI_RESET_WARM;
>         return true;
> }
>
>
>At minimum the comment is stale: "modern" platforms, *especially* when=20
>the only bootup method is EFI, as in the ACER laptop case, I think the=20
>preferred reboot method is absolutely an EFI reboot - and it's probably
>
>what Windows uses too=2E
>
>The question is, is acpi_gbl_reduced_hardware false on the Acer=20
>TravelMate X514-51T? I think it has to be, for the quirk to make sense
>-=20
>if it's true then efi_reboot_required() would set the reboot method to=20
>EFI=2E
>
>I=2Ee=2E we seem to have a new category of systems that are advertising=
=20
>themselves as 'full ACPI compliant', which are NOT old EFI systems, but
>
>modern EFI systems=2E
>
>Is there some good way to detect these - such as ACPI version or=20
>something?
>
>Thanks,
>
>	Ingo

That is exactly what the reduced hardware flag is supposed to indicate=2E =
As far as what Windows does, the are only two ways to find out: testing som=
ehow, or these days Microsoft might actually answer if we ask nicely=2E
--=20
Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E