From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753992Ab0JMO5M (ORCPT ); Wed, 13 Oct 2010 10:57:12 -0400 Received: from cantor2.suse.de ([195.135.220.15]:37443 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753944Ab0JMO5L (ORCPT ); Wed, 13 Oct 2010 10:57:11 -0400 From: Oliver Neukum Organization: SUSE To: Casey Dahlin Subject: Re: A question about ZONE_DMA Date: Wed, 13 Oct 2010 16:57:07 +0200 User-Agent: KMail/1.13.5 (Linux/2.6.36-rc7esata-12-desktop+; KDE/4.4.4; x86_64; ; ) Cc: linux-kernel@vger.kernel.org References: <20101013145240.GE12467@foucault.redhat.com> In-Reply-To: <20101013145240.GE12467@foucault.redhat.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201010131657.07187.oneukum@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Mittwoch, 13. Oktober 2010, 16:52:41 schrieb Casey Dahlin: > Hi all, > > So if I understand correctly, ZONE_DMA exists to separate and preserve the > chunk of memory to which older ISA cards are capable of doing DMA. The question > that arises for me is: > > 1) Why do /all/ 32-bit boxes have a ZONE_DMA when surely only a tiny and > shrinking number of them have a need for it? You don't know before you load the module of the driver that needs it. > 2) Why do /any/ 64-bit boxes have a ZONE_DMA? Is there really some godless > monster out there who put an early ISA bridge and a 64-bit CPU on the same > motherboard?! Parports can use DMA and are generally ISA. Regards Oliver