From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1O52UY-0008RX-QQ for qemu-devel@nongnu.org; Thu, 22 Apr 2010 15:55:18 -0400 Received: from [140.186.70.92] (port=49489 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1O52UX-0008Pb-5t for qemu-devel@nongnu.org; Thu, 22 Apr 2010 15:55:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1O52UV-0002w1-Ug for qemu-devel@nongnu.org; Thu, 22 Apr 2010 15:55:17 -0400 Received: from mail-vw0-f45.google.com ([209.85.212.45]:61054) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1O52UV-0002vo-RB for qemu-devel@nongnu.org; Thu, 22 Apr 2010 15:55:15 -0400 Received: by vws18 with SMTP id 18so187597vws.4 for ; Thu, 22 Apr 2010 12:55:15 -0700 (PDT) Sender: Richard Henderson Message-ID: <4BD0A994.2090608@twiddle.net> Date: Thu, 22 Apr 2010 12:55:00 -0700 From: Richard Henderson MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 0/2] [RFC] 64-bit io paths References: In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Blue Swirl Cc: agraf@suse.de, qemu-devel@nongnu.org, paul@codesourcery.com On 04/22/2010 12:38 PM, Blue Swirl wrote: > Subpages are used when there are several devices on the same page. > It's needed for at least Sparc32. That's fine. > Subwidth (with NULL) is used mainly to indicate that the device does > not accept accesses in some access widths. Sparc32 and Sparc64 need > this (or some other way to signal bus errors for bad access widths). This is also fine. Although by using NULL all you'd get is a qemu null pointer dereference; I suppose this might get caught and translated to an cpu exception, but I think it would be preferable long-term to be more explicit about this and fill in the entries with a function that would explicitly raise the exception. What this *does* confirm for me is that we don't need to support multiple devices at the same address, differentiated by the size of the reference. Which is something that the current subpage implementation actually supports. I'll submit a patch to clean this up. > In fact, many system devices on Sparc64 should only accept 64 bit > accesses, but currently we can't enforce this. Cool. This is something that should be fixed by the end result of the driver interface re-design that pbrook and I have been discussing on IRC. r~