From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Hancock Subject: r8169 64-bit DMA support Date: Sun, 20 Sep 2009 17:38:20 -0600 Message-ID: <4AB6BCEC.3070001@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Francois Romieu To: netdev Return-path: Received: from mail-yx0-f199.google.com ([209.85.210.199]:37036 "EHLO mail-yx0-f199.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751577AbZITXiU (ORCPT ); Sun, 20 Sep 2009 19:38:20 -0400 Received: by yxe37 with SMTP id 37so2568582yxe.33 for ; Sun, 20 Sep 2009 16:38:23 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: The r8169 driver currently disables 64-bit DMA support by default (needs a module parameter to turn it on). This is a bit sub-optimal these days with most new systems using more than 4GB of RAM. It was this patch back in 2004 that disabled it: http://git.kernel.org/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commitdiff;h=c525e7cf69bfe18a1bf362558be5398e0b925d07 It's not clear (from the mails I've read) exactly what was going on in the case that caused this to be added. Normally these days the PCI subsystem is supposed to detect that DAC isn't usable on a machine and refuse setting 64-bit DMA masks, it's not the driver's responsibility to handle this. I'm guessing that when this change was made that detection didn't exist though. Thoughts on whether this default can be changed now? Or at least for the PCI Express devices, which really should have nothing special about 64-bit addressing..