Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755091AbaFJGyi (ORCPT ); Tue, 10 Jun 2014 02:54:38 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:1520 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754776AbaFJGyh (ORCPT ); Tue, 10 Jun 2014 02:54:37 -0400 Message-ID: <5396AB30.10607@huawei.com> Date: Tue, 10 Jun 2014 14:52:32 +0800 From: Liu hua User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.0.1 MIME-Version: 1.0 To: Nicolas Pitre , Rob Herring CC: Russell King - ARM Linux , , Laura Abbott , , Will Deacon , "linux-kernel@vger.kernel.org" , , Santosh Shilimkar , , , "linux-arm-kernel@lists.infradead.org" , Rabin Vincent Subject: Re: [PATCH v3 2/2] ARM : change fixmap mapping region to support 32 CPUs References: <1397559967-26050-1-git-send-email-sdu.liu@huawei.com> <1397559967-26050-3-git-send-email-sdu.liu@huawei.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.111.58.238] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014/5/31 3:25, Nicolas Pitre Wrote: > On Fri, 30 May 2014, Rob Herring wrote: > >> There's work in flight to support early_ioremap, early console, and RO >> text patching which all use the fixmap region. >> >> There's a couple of options to solve this: >> >> - Only support up to 16 cpus. It could be anywhere between 17-31, but >> that seems somewhat unlikely. Are we really ever going to see 32-bit >> 32 core systems? > > I wouldn't rule that out. I've seen 16-core ARM chips in 2008 (although > they didn't go into production). Silly limitations like that always > come back to bite you. And we have better alternatives.New Now our team is woring on arma15 with 16 CPUs. > >> - Reduce KM_TYPE_NR from 16 to 15. Based on the comment for it, we >> probably don't want to do that. Is increasing it to the default of 20 >> worthwhile? Some of the options here would allow doing that. >> - Add 0xffe00000-0xfff00000 to the fixmap region. This would make >> fixmap span 2 PMDs with the top PMD having a mixture of uses like we >> had before. > > That would be my preferred approach. Note here it could be > 0xffe00000-0xfffe0000 to include the whole of the previous fixmap area > curently unused. > >> - push the PCI i/o space down to 0xfec00000 and make fixmap 4MB. This >> is a cleaner solution as the 2 PMDs are only used for fixmap. This may >> require some static mapping adjustments on some platforms. > > No need. With the latest changes, the fixmap area is between 0xffc00000 > and 0xffe00000 (there is apparently a mistake in > Documentation/arm/memory.txt). So currently 0xff000000-0xffc00000 is > free, which makes the fixmap area far away from the PCI i/o area with > plenti of space in between. > >> - Same as previous option, but convert the PCI i/o space to fixmap >> entries. We don't really need all 2MB for PCI. > > See above. > >> Also, there is an error in the documentation below: >> >>> >>> Signed-off-by: Liu Hua >>> --- >>> Documentation/arm/memory.txt | 2 +- > > Yep, good that you spotted it as well. I failed to catch it during my > review so I'll send a patch. > Very sorry for the mistake and ignoreing this mail. Maybe I should imporve my email client! Thanks again for Nicolas. Thanks, Liu Hua > > Nicolas > > . > -- 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/