From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Gibson Subject: Re: question about dma-ranges Date: Wed, 27 Oct 2010 13:42:27 +1100 Message-ID: <20101027024227.GD7023@yookeroo> References: <9696D7A991D0824DBA8DFAC74A9C5FA306911C5F@az33exm25.fsl.freescale.net> <4CC77784.2070701@firmworks.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org To: Timur Tabi Cc: Yoder Stuart-B08248 , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org List-Id: devicetree@vger.kernel.org On Tue, Oct 26, 2010 at 08:37:55PM -0500, Timur Tabi wrote: > On Tue, Oct 26, 2010 at 7:51 PM, Mitch Bradley wrote: > > =A0It's probably unnecessary on modern machines, but old PCs were fairly > > restrictive about DMA addresses due to short counters. =A0The buses on = which > > such restrictions applied are no longer at the root level, but they were > > once there... > = > It's still necessary. The QE, which we ship on several of our current > parts, can only DMA to/from 32-bit addresses, even on SOCs that > support 36-bit addressing for everything else. But the QE is not at the top-level, IIRC, so its restrictions can be encoded in the dma-ranges on its own bus. We're talking specifically about the special case of dma-ranges in the root node, not the utility of dma-ranges in general which is clear. -- = David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson