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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id u14sm49794926wrr.1.2019.04.16.23.16.51 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 16 Apr 2019 23:16:52 -0700 (PDT) Date: Wed, 17 Apr 2019 08:16:50 +0200 From: Ingo Molnar To: Daniel Drake Cc: Peter Zijlstra , Borislav Petkov , Thomas Gleixner , Linux Kernel , Linus Torvalds , Jian-Hong Pan , matt@codeblueprint.co.uk, Ard Biesheuvel , hpa@zytor.com, linux-efi@vger.kernel.org, Len Brown , linux-tip-commits@vger.kernel.org, Endless Linux Upstreaming Team Subject: Re: EFI reboot vs. ACPI reboot (was: Re: [tip:x86/urgent] x86/reboot, efi: Use EFI reboot for Acer TravelMate X514-51T) Message-ID: <20190417061650.GA31060@gmail.com> References: <20190412080152.3718-1-jian-hong@endlessm.com> <20190416082042.GA69717@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Daniel Drake wrote: > On Tue, Apr 16, 2019 at 4:20 PM Ingo Molnar wrote: > > I wanted to get a second opinion from the EFI folks for this whole > > concept. On x86 we default to ACPI reboot on modern systems, and we > > default to EFI reboot on modern EFI systems, via the > > efi_reboot_required() method which keys off on acpi_gbl_reduced_hardware > > to create a barrier for older ACPI systems. > > So if acpi_gbl_reduced_hardware is set, we are on a "modern EFI > system", and EFI reboot is used. > > > It appears that Acer TravelMate X514-51T systems get marked as > > 'acpi_gbl_reduced_hardware' which enables ACPI-reboot, but they require > > EFI-reboot. > > We will double check, but in this case I believe the system is *not* > marked as reduced hardware, which is why ACPI reboot is used. 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. > > Should we perhaps re-think the boundary between EFI-reboot and > > ACPI-reboot systems? I.e. if the EFI runtime is enabled, shouldn't we > > just use the EFI reboot method? > > I agree this is a good question. > > We also previously hit a similar issue for shutdown on Acer laptops > which is still unresolved. > https://marc.info/?l=linux-acpi&m=148857214431346&w=2 Yeah. Feel free to send a patch that makes EFI reboot the default one under these circumstances, we could put it into tip:x86/platform or so, and let it get tested for another kernel cycle. If it's problem-free we could push that upstream. (Famous last words.) (This won't affect the ACER notebook quirk in tip:x86/urgent, which is the short-term solution and the -stable tag.) Thanks, Ingo