From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753013AbXLHUpK (ORCPT ); Sat, 8 Dec 2007 15:45:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754636AbXLHUoq (ORCPT ); Sat, 8 Dec 2007 15:44:46 -0500 Received: from ftp.linux-mips.org ([194.74.144.162]:41192 "EHLO ftp.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754627AbXLHUoo (ORCPT ); Sat, 8 Dec 2007 15:44:44 -0500 Date: Sat, 8 Dec 2007 20:44:26 +0000 From: Ralf Baechle To: Kumar Gala Cc: davem@davemloft.net, wli@holomorphy.com, mingo@redhat.com, linux-kernel@vger.kernel.org, Benjamin Herrenschmidt Subject: Re: use of fixmap on non-x86/sh? Message-ID: <20071208204426.GC3361@linux-mips.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 30, 2007 at 04:14:55PM -0600, Kumar Gala wrote: > Ben and I are talking about using fixmap on ppc for similar applications to > it use on x86. However in poking around other arch's (sparc, mips) they > appear to have some support but not as complete as x86. > > For example both SPARC & MIPS reference __set_fixmap() in asm/fixmap.h but > I can't find an implementation on either. > > So I was wondering if there was some reason fixmap isn't as well supported > or if its just used for a specific function on those SPARC, MIPS, etc. and > they dont need as much functionality out of it as x86 does. MIPS uses fixmap for two purposes: o In some cases it is possibly to avoid or optimize a cacheflush by creating a temporary mapping. The mechanism works very similar to what x86 and MIPS use for atomic kmaps. o Highmem. Both manipulate pagetables directly or even insert entries directly into the TLB without pagetables as intermediate stage so __set_fixmap is indeed unused. Ralf