From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=42137 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PJ2jw-0002lA-RG for qemu-devel@nongnu.org; Thu, 18 Nov 2010 06:33:22 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PJ2jv-0008Aw-C5 for qemu-devel@nongnu.org; Thu, 18 Nov 2010 06:33:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:3560) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PJ2jv-0008Aq-3q for qemu-devel@nongnu.org; Thu, 18 Nov 2010 06:33:19 -0500 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id oAIBXIDN026848 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Thu, 18 Nov 2010 06:33:18 -0500 Date: Thu, 18 Nov 2010 13:33:08 +0200 From: "Michael S. Tsirkin" Subject: Re: [Qemu-devel] Re: [PATCH] spice: add qxl device Message-ID: <20101118113308.GC31261@redhat.com> References: <20101117135842.GA13690@redhat.com> <4CE3F2CD.4030701@redhat.com> <20101117164244.GE27909@redhat.com> <4CE40AAF.7090202@redhat.com> <20101117180008.GE29556@redhat.com> <20101118080935.GW7948@redhat.com> <20101118090321.GD16832@redhat.com> <20101118091149.GY7948@redhat.com> <20101118093026.GG16832@redhat.com> <20101118095751.GA7948@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20101118095751.GA7948@redhat.com> Content-Transfer-Encoding: quoted-printable List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Natapov Cc: Gerd Hoffmann , qemu-devel@nongnu.org On Thu, Nov 18, 2010 at 11:57:51AM +0200, Gleb Natapov wrote: > On Thu, Nov 18, 2010 at 11:30:27AM +0200, Michael S. Tsirkin wrote: > > On Thu, Nov 18, 2010 at 11:11:49AM +0200, Gleb Natapov wrote: > > > On Thu, Nov 18, 2010 at 11:03:21AM +0200, Michael S. Tsirkin wrote: > > > > On Thu, Nov 18, 2010 at 10:09:35AM +0200, Gleb Natapov wrote: > > > > > On Wed, Nov 17, 2010 at 08:00:08PM +0200, Michael S. Tsirkin wr= ote: > > > > > > > >> If so: does qemu > > > > > > > >>emulate this correctly? > > > > > > > > > > > > > > > >It mostly does. > > > > > > >=20 > > > > > > > I doubt it actually enables/disables the legacy vga ports. > > > > > >=20 > > > > > > I'll check when I have the time. We can fix it if it doesn't, > > > > > >=20 > > > > > So many guests (all of them?) just assume that vga ports and > > > > > framebuffer is there. > > > >=20 > > > > Why do you think they disable io memory then? > > > >=20 > > > Who and how and when disables io memory? > >=20 > > I think guest will do this if you disable the device through the devi= ce > > manager. This might need a reboot to become effective. > >=20 > Try to do it with primary VGA adapter and tell us what happens :) >=20 > > > Some guests are designed to run > > > even on old ISA machines that have no way to disable anything. The > > > device is just there. > > >=20 > > > This is the same with IDE ports. BIOS "knows" legacy ISA ports and = just > > > program them into PCI IO bars to be nice. > >=20 > > HAven't checked IDE, for VGA AFAIK BIOS does not program legacy ports= in > > the card, they are hardwired there. However, the card must not claim = any > > io transactions if IO memory is disabled in command register. > >=20 > Is this correct also for legacy ports? Yes. The spec is quite explicit on this point: A function that supports a PC legacy function (IDE, VGA, etc.) is allowed to claim those addresses associated with the specific function when the I/O Space (see Figure 6-2) enable bit is set. These addresses are not requested using a Base Address register but are assigned by initialization software. If a device identifies itself as a legacy function (class code), the initialization software grants the device permission to claim the I/O legacy addresses by setting the device=E2=80=99= s I/O Space enable bit. > This wouldn't be backwards > compatible to ISA machines, so old software my not run properly back in > the days when transaction from ISA to PCI happened. initialization software could be the BIOS. So maybe BIOS update was needed in the transition. > So my guess is that > old ISA ports works in backwards compatible way. The spec seems to contradict this. > > When qemu is started, it works correctly: the io memory is disabled a= nd card does > > not claim any io. Then BIOS comes along and enables io. At this point > > map callback is invoked and maps io memory, card starts claiming io. > Looking at the code I see that cirrus claims all IO ports and > framebuffer memory during init function unconditionally. So that may be OK for ISA, but not for PCI. > >=20 > > What is broken is that if BIOS/guest then disables IO memory, > > (I think - even if guest is rebooted!) we will keep claiming IO trans= actions. > > That our emulation does this seems to be a clear spec violation, we a= re > > just lucky that BIOS/guest does not do this at the moment. > >=20 > >=20 > >=20 > > > > > So what "fixing" this will buy us? > > > >=20 > > > > Besides spec compliancy, you mean? Ability to support multiple V= GA > > > > cards. That's how it works I think: BIOS enables IO on the primar= y > > > > VGA device only. > > > >=20 > > > What spec defines hot-plug for primary VGA adapter? > >=20 > > No idea about hotplug. I am talking about multiple VGA cards, > > enabling/disabling them dynamically should be possible. > Of course. With properly designed VGA card you should be able to have > more then one, And, for that to have a chance to work when all cards are identical, you don't claim IO when IO is disabled. > but one of them will provide legacy functionality > and is not removable. The guest might not support hotplug. But there's no way it can prevent surprise removal. qemu should not crash when this happens. > >=20 > > > Our BIOS should support > > > -M isa machine too. > >=20 > > > There is no way to disable VGA or even check if it > > > is present there. > >=20 > > So I guess with isa you can't have multiple VGA cards work. With PCI > > I think you can. > >=20 > With isa you just need custom designed HW and software and you can have > as many VGA cards as you want :) >=20 > -- > Gleb.