From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 3 Jul 2001 04:07:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 3 Jul 2001 04:07:18 -0400 Received: from t2.redhat.com ([199.183.24.243]:60662 "HELO executor.cambridge.redhat.com") by vger.kernel.org with SMTP id ; Tue, 3 Jul 2001 04:07:03 -0400 To: Jeff Garzik Cc: David Howells , Alan Cox , linux-kernel@vger.kernel.org Subject: Re: [RFC] I/O Access Abstractions In-Reply-To: Message from Jeff Garzik of "Tue, 03 Jul 2001 04:00:09 EDT." <3B417B89.6FE1D06A@mandrakesoft.com> Date: Tue, 03 Jul 2001 09:07:02 +0100 Message-ID: <3938.994147622@warthog.cambridge.redhat.com> From: David Howells Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > David Howells wrote: > > For example, one board I've got doesn't allow you to do a straight > > memory-mapped I/O access to your PCI device directly, but have to > > reposition a window in the CPU's memory space over part of the PCI memory > > space first, and then hold a spinlock whilst you do it. > > Yuck. Does that wind up making MMIO slower than PIO, on this board? The mapping is not symmetrical (things on the PCI bus can see more of the CPU bus at any one time than the reverse, so DMA isn't a problem), and at the moment I have only one device on it that I'm actually using (the ethernet chipset). David