From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762498AbXGZKph (ORCPT ); Thu, 26 Jul 2007 06:45:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756276AbXGZKp1 (ORCPT ); Thu, 26 Jul 2007 06:45:27 -0400 Received: from ua-85-227-1-9.cust.bredbandsbolaget.se ([85.227.1.9]:57261 "EHLO omoikane.mc.pp.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756116AbXGZKp0 (ORCPT ); Thu, 26 Jul 2007 06:45:26 -0400 X-Greylist: delayed 2091 seconds by postgrey-1.27 at vger.kernel.org; Thu, 26 Jul 2007 06:45:26 EDT To: "Peter Bortas" Cc: "Adrian McMenamin" , "Andrew Morton" , linux-kernel@vger.kernel.org, lethal@users.sourceforge.net Subject: Re: [PATCH] Fix DMA on Dreamcast References: <92a12cdb0707191230g216feaf2ied3e95bacf4dd572@mail.gmail.com> <20070720120408.1f190269.akpm@linux-foundation.org> <92a12cdb0707210322m6670acaer768d078c5e358b0c@mail.gmail.com> <7e5f60720707210424w48f9dc10hff044d702f7bd1d3@mail.gmail.com> <92a12cdb0707210506t5cf58cc4gc5b70f335545dc3f@mail.gmail.com> <7e5f60720707210713o4ff0825eu463abee77dc1f04c@mail.gmail.com> From: Marcus Comstedt Date: Thu, 26 Jul 2007 12:10:30 +0200 In-Reply-To: <7e5f60720707210713o4ff0825eu463abee77dc1f04c@mail.gmail.com> (Peter Bortas's message of "Sat, 21 Jul 2007 16:13:19 +0200") Message-ID: User-Agent: Gnus/5.1007 (Gnus v5.10.7) XEmacs/21.4.19 (linux) 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 "Peter Bortas" writes: > On 7/21/07, Adrian McMenamin wrote: >> On 21/07/07, Peter Bortas wrote: >> >> > >> > Sidenote: Does Linux handle the Dreamcast DMA errata? >> > >> >> You need to explain what you mean (at least to me!). >> >> If you mean will it degrade gracefully - not without this patch if set >> to the (correct) defconfig. With iffy settings it will. > > If I remember correctly (and that's a big if since I last looked at it > in 2001) some revisions of the Dreamcast hardware would sporadically > lock up if you scheduled a new DMA request to quickly after a previous > one, even if you checked the ready bit. It's worked around by a delay > of X microseconds as recommended by Sega engineers. I don't remember > the value of X, nor where exactly in the flow this workaround should > be applied. > > Adding Marcus in case he has a better memory than me. I don't remeber any such delay. Are you sure you're not thinking about the G2 bus problem (where accesses need to be programatically serialized, whether they are PIO or DMA)? // Marcus