From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57419) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZIGoc-00029h-Ku for qemu-devel@nongnu.org; Thu, 23 Jul 2015 09:45:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZIGoY-0004TZ-1s for qemu-devel@nongnu.org; Thu, 23 Jul 2015 09:45:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51282) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZIGoX-0004TU-Qd for qemu-devel@nongnu.org; Thu, 23 Jul 2015 09:45:33 -0400 References: <1437494626-3773-1-git-send-email-markmb@redhat.com> <1437494626-3773-3-git-send-email-markmb@redhat.com> <20150722042434.GB27877@morn.localdomain> <20150722103112.1d97386b@markmb_rh> <20150722171804.GA2717@morn.localdomain> <55B0E86E.2030209@redhat.com> From: Laszlo Ersek Message-ID: <55B0EFF5.1050608@redhat.com> Date: Thu, 23 Jul 2015 15:45:25 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC 2/7] fw_cfg dma interface List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Stefan Hajnoczi , QEMU Developers , "Richard W.M. Jones" , Kevin O'Connor , Gerd Hoffmann , Paolo Bonzini , =?UTF-8?Q?Marc_Mar=c3=ad?= On 07/23/15 15:35, Peter Maydell wrote: > On 23 July 2015 at 14:13, Laszlo Ersek wrote: >> On 07/22/15 19:18, Kevin O'Connor wrote: >>> Another possibility would be to place the new fw_cfg dma register >>> address into a named fw_cfg "file" (eg, "fw_cfg_dma"). The firmware >>> could then use the existing select/data fw_cfg interface to check if >>> the new dma interface is available by scanning for that "fw_cfg_dma" >>> file. This has the advantage of not requiring a new "magic address", >>> but has the disadvantage of a more complex probe. >> >> I like this one so much that I'm worried I'm missing some details. :) > > This requires the device itself to know its own address, which > is in QEMU possible but ugly enough to be worth avoiding. > > For ARM MMIO the obvious answer is "the new register should > just go next to the first one". Does x86 do something that > means we can't put it somewhere equally straightforward > or do discovery via whatever x86 uses for discovering MMIO? I don't know how x86 determines the MMIO mapping. As far as I gather from the SeaBIOS patches and this QEMU series, 0xfef00000 is a hand-picked fixed address. (See BIOS_CFG_DMA_ADDR in 7/7.) 0xfef00000 seems to fall right above the 1MB LAPIC range; I guess there's no conflict with anything else... Thanks Laszlo