From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754016Ab2ILWyx (ORCPT ); Wed, 12 Sep 2012 18:54:53 -0400 Received: from arroyo.ext.ti.com ([192.94.94.40]:57028 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751667Ab2ILWyu (ORCPT ); Wed, 12 Sep 2012 18:54:50 -0400 Message-ID: <505112A3.7080703@ti.com> Date: Wed, 12 Sep 2012 18:54:27 -0400 From: Cyril Chemparathy User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:15.0) Gecko/20120907 Thunderbird/15.0.1 MIME-Version: 1.0 To: Greg KH CC: , , , , , , , , , , , , , Subject: Re: [PATCH v2] /dev/mem: use phys_addr_t for physical addresses References: <1347473158-7219-1-git-send-email-cyril@ti.com> <20120912181503.GB12840@kroah.com> In-Reply-To: <20120912181503.GB12840@kroah.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Greg, On 9/12/2012 2:15 PM, Greg KH wrote: > On Wed, Sep 12, 2012 at 02:05:58PM -0400, Cyril Chemparathy wrote: >> This patch fixes the /dev/mem driver to use phys_addr_t for physical >> addresses. This is required on PAE systems, especially those that run >> entirely out of >4G physical memory space. > > What is the symptom if this patch is not applied? Does it need to be > backported to older kernels? If so, which ones? > As far as I can tell, this change only benefits platforms where lowmem lies outside the 32-bit addressable range. On the ARM based KeyStone platform, all of our memory is located above the 4GB limit at 0x8:0000:0000. On this platform, trying to read lowmem breaks as follows: # dd if==/dev/mem of=/dev/null bs==4k count=1 skip=8388608 dd: /dev/mem: Bad address Assuming that we are unique in this regard (i.e. lowmem outside 4GB), I don't see any reason to backport this to earlier kernels. -- Thanks - Cyril