From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752522AbdLHIwt (ORCPT ); Fri, 8 Dec 2017 03:52:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:38965 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750927AbdLHIws (ORCPT ); Fri, 8 Dec 2017 03:52:48 -0500 Subject: Re: [PATCH v2 1/3] x86/boot: add acpi rsdp address to setup_header To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, boris.ostrovsky@oracle.com, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, corbet@lwn.net, rjw@rjwysocki.net, lenb@kernel.org, linux-acpi@vger.kernel.org References: <20171207122821.30158-1-jgross@suse.com> <20171207122821.30158-2-jgross@suse.com> <20171208071653.mzyf3ct6n6h2x37r@gmail.com> <81777128-a277-c47b-2570-a330b2f6c50d@suse.com> <20171208084827.yv3vrtfnn6otjdg4@gmail.com> From: Juergen Gross Message-ID: <492e188d-6985-fb13-278b-46f096cb1b4b@suse.com> Date: Fri, 8 Dec 2017 09:52:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171208084827.yv3vrtfnn6otjdg4@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/12/17 09:48, Ingo Molnar wrote: > > * Juergen Gross wrote: > >>>> +Offset/size: 0x268/8 >>>> +Protocol: 2.14+ >>>> + >>>> + This field can be set by the boot loader to tell the kernel the >>>> + physical address of the ACPI RSDP table. >>>> + >>>> + A value of 0 indicates the kernel should fall back to the standard >>>> + methods to locate the RSDP (search in EBDA/low memory). >>> >>> That's not the only method used: the ACPI RSDP address can also be discovered via >>> efi.rsdp20 and efi.rsdp, both of which appear to be 32-bit values. >> >> Sure, but this is valid for booting via EFI only. > > Yeah, so what I tried to say is that the description as written is not fully > correct and triggered my pedantry: > > + A value of 0 indicates the kernel should fall back to the standard > + methods to locate the RSDP (search in EBDA/low memory). > > To make it correct we need to either write less: > > + A value of 0 indicates the kernel should fall back to the standard > + methods to locate the RSDP. > > or write more and make it open ended so it doesn't have to be extended with every > method of getting the RSDP that might be added in the future: > > + A value of 0 indicates the kernel should fall back to the standard > + methods to locate the RSDP (search in EBDA/low memory, get it from > + EFI if present, etc.). > > ... or so? Aah, okay. I got your remark wrong then. I think I'll go with the shorter variant. Juergen