From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64 Date: Fri, 9 Jan 2015 15:13:43 +0000 Message-ID: <20150109151342.GE24408@e104818-lin.cambridge.arm.com> References: <1413553034-20956-1-git-send-email-hanjun.guo@linaro.org> <1610983.9vqJdsL27R@wuerfel> <20150109103307.GC24408@e104818-lin.cambridge.arm.com> <3341506.a2BFqPNg3k@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <3341506.a2BFqPNg3k@wuerfel> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Rob Herring , Daniel Lezcano , Robert Richter , Jason Cooper , "linaro-acpi@lists.linaro.org" , Marc Zyngier , "jcm@redhat.com" , Randy Dunlap , Liviu Dudau , Robert Moore , Will Deacon , "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , Mark Brown , "Rafael J. Wysocki" , Lv Zheng , Bjorn Helgaas , Olof Johansson List-Id: linux-acpi@vger.kernel.org On Fri, Jan 09, 2015 at 10:55:51AM +0000, Arnd Bergmann wrote: > On Friday 09 January 2015 10:33:07 Catalin Marinas wrote: > > On Wed, Jan 07, 2015 at 07:48:48PM +0000, Arnd Bergmann wrote: > > > > In other cases that's actually a good thing. One such example is the > > > "Principles of ARM Memory Maps" document that tells hardware implementers > > > to do a rather complex mapping "To support 36-bit x86 PAE compatible operating > > > systems, such as Linux." but makes life much harder in the process than > > > any of the random mappings we have seen in the wild. > > > > Unfortunately, with any significant amount of RAM (say 16GB), this > > document becomes pretty useless. It basically forces you to have a very > > sparse physical address map from 0 to over 40-bit. I wouldn't apply the > > ARM memory maps doc to server systems. > > Are you sure? I was under the impression that this document was targetted > specifically at servers. Ah, sorry for the confusion, I haven't read the latest (apparently from 2012) update which covers 44 and 48-bit memory maps. The only downside is that for more than 32GB of RAM (up to 512GB) it requires a 40-bit memory map. Given the sparseness, we can't use 3-levels of page table with 4KB pages which can only cover 39-bit. Anyway, not a major issue. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932460AbbAIPOD (ORCPT ); Fri, 9 Jan 2015 10:14:03 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:58832 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932149AbbAIPN7 (ORCPT ); Fri, 9 Jan 2015 10:13:59 -0500 Date: Fri, 9 Jan 2015 15:13:43 +0000 From: Catalin Marinas To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Rob Herring , Daniel Lezcano , Robert Richter , Jason Cooper , "linaro-acpi@lists.linaro.org" , Marc Zyngier , "jcm@redhat.com" , Randy Dunlap , Liviu Dudau , Robert Moore , Will Deacon , "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , Mark Brown , "Rafael J. Wysocki" , Lv Zheng , Bjorn Helgaas , Olof Johansson Subject: Re: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64 Message-ID: <20150109151342.GE24408@e104818-lin.cambridge.arm.com> References: <1413553034-20956-1-git-send-email-hanjun.guo@linaro.org> <1610983.9vqJdsL27R@wuerfel> <20150109103307.GC24408@e104818-lin.cambridge.arm.com> <3341506.a2BFqPNg3k@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3341506.a2BFqPNg3k@wuerfel> Thread-Topic: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64 Accept-Language: en-GB, en-US Content-Language: en-US User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 09, 2015 at 10:55:51AM +0000, Arnd Bergmann wrote: > On Friday 09 January 2015 10:33:07 Catalin Marinas wrote: > > On Wed, Jan 07, 2015 at 07:48:48PM +0000, Arnd Bergmann wrote: > > > > In other cases that's actually a good thing. One such example is the > > > "Principles of ARM Memory Maps" document that tells hardware implementers > > > to do a rather complex mapping "To support 36-bit x86 PAE compatible operating > > > systems, such as Linux." but makes life much harder in the process than > > > any of the random mappings we have seen in the wild. > > > > Unfortunately, with any significant amount of RAM (say 16GB), this > > document becomes pretty useless. It basically forces you to have a very > > sparse physical address map from 0 to over 40-bit. I wouldn't apply the > > ARM memory maps doc to server systems. > > Are you sure? I was under the impression that this document was targetted > specifically at servers. Ah, sorry for the confusion, I haven't read the latest (apparently from 2012) update which covers 44 and 48-bit memory maps. The only downside is that for more than 32GB of RAM (up to 512GB) it requires a 40-bit memory map. Given the sparseness, we can't use 3-levels of page table with 4KB pages which can only cover 39-bit. Anyway, not a major issue. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Fri, 9 Jan 2015 15:13:43 +0000 Subject: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64 In-Reply-To: <3341506.a2BFqPNg3k@wuerfel> References: <1413553034-20956-1-git-send-email-hanjun.guo@linaro.org> <1610983.9vqJdsL27R@wuerfel> <20150109103307.GC24408@e104818-lin.cambridge.arm.com> <3341506.a2BFqPNg3k@wuerfel> Message-ID: <20150109151342.GE24408@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Jan 09, 2015 at 10:55:51AM +0000, Arnd Bergmann wrote: > On Friday 09 January 2015 10:33:07 Catalin Marinas wrote: > > On Wed, Jan 07, 2015 at 07:48:48PM +0000, Arnd Bergmann wrote: > > > > In other cases that's actually a good thing. One such example is the > > > "Principles of ARM Memory Maps" document that tells hardware implementers > > > to do a rather complex mapping "To support 36-bit x86 PAE compatible operating > > > systems, such as Linux." but makes life much harder in the process than > > > any of the random mappings we have seen in the wild. > > > > Unfortunately, with any significant amount of RAM (say 16GB), this > > document becomes pretty useless. It basically forces you to have a very > > sparse physical address map from 0 to over 40-bit. I wouldn't apply the > > ARM memory maps doc to server systems. > > Are you sure? I was under the impression that this document was targetted > specifically at servers. Ah, sorry for the confusion, I haven't read the latest (apparently from 2012) update which covers 44 and 48-bit memory maps. The only downside is that for more than 32GB of RAM (up to 512GB) it requires a 40-bit memory map. Given the sparseness, we can't use 3-levels of page table with 4KB pages which can only cover 39-bit. Anyway, not a major issue. -- Catalin