Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S268204AbUIPUHM (ORCPT ); Thu, 16 Sep 2004 16:07:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S268183AbUIPUHM (ORCPT ); Thu, 16 Sep 2004 16:07:12 -0400 Received: from omx1-ext.sgi.com ([192.48.179.11]:30100 "EHLO omx1.americas.sgi.com") by vger.kernel.org with ESMTP id S268213AbUIPUGv (ORCPT ); Thu, 16 Sep 2004 16:06:51 -0400 Date: Thu, 16 Sep 2004 13:05:15 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Robert Picco cc: Bjorn Helgaas , linux-kernel@vger.kernel.org, Jesse Barnes , venkatesh.pallipadi@intel.com Subject: Re: device driver for the SGI system clock, mmtimer In-Reply-To: <4149D655.5070904@hp.com> Message-ID: References: <200409161003.39258.bjorn.helgaas@hp.com> <200409161054.51467.bjorn.helgaas@hp.com> <4149D655.5070904@hp.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1310 Lines: 28 On Thu, 16 Sep 2004, Robert Picco wrote: > >Is there something specific that drivers/char/hpet.c expects that > >your hardware doesn't implement? > Look at HPET revision history. Specifically 0.98 01/20/2002 > * Product name changed: from Multimedia Timer to HPET (High > Precision Event Timer) The HPET timer has a specific memory layout of registers that is mappable to user space. The mmtimer driver only allows the mapping of a single 64 bit counter to use space. We have lots of applications at SGI that rely on mmtimer since mmtimer provides a locally accessible clock in an NUMA environment with hundreds of CPU. A hpet device would have to show up in the global address space and require cross node accesses in our NUMA environment that would make access to the timer slow. All CPU would content for access to a certain global memory address. The HPET hardware and the sgi mmtimer are totally different architectures that are not easily reconcilable. The software API to handle both is similar and we would like it to be as compatible as possible. - 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/