Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765560AbXLNVH4 (ORCPT ); Fri, 14 Dec 2007 16:07:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756014AbXLNVHr (ORCPT ); Fri, 14 Dec 2007 16:07:47 -0500 Received: from mga01.intel.com ([192.55.52.88]:18370 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753319AbXLNVHq (ORCPT ); Fri, 14 Dec 2007 16:07:46 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.24,169,1196668800"; d="scan'208";a="439429872" Date: Fri, 14 Dec 2007 13:06:45 -0800 From: "Siddha, Suresh B" To: "Eric W. Biederman" Cc: venkatesh.pallipadi@intel.com, ak@muc.de, rdreier@cisco.com, torvalds@linux-foundation.org, gregkh@suse.de, airlied@skynet.ie, davej@redhat.com, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, akpm@linux-foundation.org, arjan@infradead.org, jesse.barnes@intel.com, linux-kernel@vger.kernel.org, Suresh Siddha Subject: Re: [RFC PATCH 02/12] PAT 64b: Basic PAT implementation Message-ID: <20071214210645.GA717@linux-os.sc.intel.com> References: <20071213235543.568682000@intel.com> <20071213235711.464325000@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1378 Lines: 32 On Thu, Dec 13, 2007 at 08:48:45PM -0700, Eric W. Biederman wrote: > > + pat = PAT(0,WB) | PAT(1,WT) | PAT(2,UC_MINUS) | PAT(3,WC) | > > + PAT(4,WB) | PAT(5,WT) | PAT(6,UC_MINUS) | PAT(7,WC); > > I strongly object to this configuration. > > The caching modes of interest are: > PAT_WB write-back or a close as the MTRRs will allow > used for WC today. > PAT_UC completely uncachable not overridable by MTRRs > and what we use today for pgprot_noncached > PAT_WC what isn't available for current use. > > We should use: > > + pat = PAT(0,WB) | PAT(1,WT) | PAT(2,WC) | PAT(3,UC) | > > + PAT(4,WB) | PAT(5,WT) | PAT(6,WC) | PAT(7,UC); > > Changing the UC- which currently allows write-combining if the MTRRs specify it, > to WC. This grandfathers in all of our current usage and changes the one > PAT type that could today and in legacy mode specify WC to really specify WC. That seems reasonable. But looking at mainline kernel, ioremap_nocache() actually uses UC_MINUS. Wonder why it is not using UC (like pgprot_noncached). I think it is ok to change ioremap_nocache() to use UC. thanks, suresh -- 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/