Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751661AbaB1F4e (ORCPT ); Fri, 28 Feb 2014 00:56:34 -0500 Received: from cavan.codon.org.uk ([93.93.128.6]:40476 "EHLO cavan.codon.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750719AbaB1F4d (ORCPT ); Fri, 28 Feb 2014 00:56:33 -0500 Date: Fri, 28 Feb 2014 05:56:29 +0000 From: Matthew Garrett To: "Li, Aubrey" Cc: "alan@linux.intel.com" , linux-kernel@vger.kernel.org, "H. Peter Anvin" , Len.Brown@intel.com, Adam Williamson Subject: Re: [patch] x86: Introduce BOOT_EFI and BOOT_CF9 into the reboot sequence loop Message-ID: <20140228055629.GA847@srcf.ucam.org> References: <53100C8D.1060001@linux.intel.com> <20140228045637.GA28257@srcf.ucam.org> <53101D1D.9010202@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53101D1D.9010202@linux.intel.com> User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: mjg59@cavan.codon.org.uk X-SA-Exim-Scanned: No (on cavan.codon.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 28, 2014 at 01:22:37PM +0800, Li, Aubrey wrote: > On 2014/2/28 12:56, Matthew Garrett wrote: > > EFI reboot is still somewhat unreliable - it may be safe after the > > recent patches to provide a 1:1 mapping. > > So it's acceptable to put EFI in the default list. Probably, once we've got those patches landed (I've lost track of whether they're in 3.13 or aimed at 3.14) > > CF9 is, as far as I know, not part of any spec, so it seems like a bad > > idea to put it in the default list. > > Any hurt known if put it in the default list? Mm. Not all x86 platforms support cf8/cf9 (Moorestown, for instance) and so it's theoretically possible that they'd put some different hardware there instead. But then, Moorestown probably has its own reboot code, so that may not matter? > > > > What do the ACPI reboot vectors look like on these systems? > > Reset register address: 0xCF9 > Value to cause reset: 0x6 Huh. But that's almost exactly what the PCI reboot code would do. Why does the PCI method work but the ACPI one fail? Does it really depend on ORing the original value with the reset value? Or is the timing just somehow marginal? > > This is definitely incorrect. The ACPI write *must* occur twice in order > > to be effective on various systems. EFI shouldn't be attempted until > > after the second ACPI write. > > > > Do we have any spec mentioned that? Nope. This is entirely unspecified, it's just how things work - several vendors use cf9 for the ACPI reboot vector, and there have to be two writes to cf9 to trigger the reboot. Windows attempts the write twice, and as a result things work. -- Matthew Garrett | mjg59@srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/