From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NuigW-0005bY-A8 for qemu-devel@nongnu.org; Thu, 25 Mar 2010 04:45:00 -0400 Received: from [140.186.70.92] (port=50487 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NuigP-0005aK-Co for qemu-devel@nongnu.org; Thu, 25 Mar 2010 04:44:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1NuigN-0003BF-Gs for qemu-devel@nongnu.org; Thu, 25 Mar 2010 04:44:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62610) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1NuigN-0003Ay-88 for qemu-devel@nongnu.org; Thu, 25 Mar 2010 04:44:51 -0400 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 o2P8inc5022447 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Thu, 25 Mar 2010 04:44:50 -0400 From: Juan Quintela In-Reply-To: <4BAB1D36.6030608@redhat.com> (Gerd Hoffmann's message of "Thu, 25 Mar 2010 09:22:14 +0100") References: <1269440070-26788-1-git-send-email-kraxel@redhat.com> <4BAA6B93.1090405@redhat.com> <4BAB1D36.6030608@redhat.com> Date: Thu, 25 Mar 2010 09:44:47 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: [Qemu-devel] Re: [PATCH] update bochs vbe interface List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: qemu-devel@nongnu.org Gerd Hoffmann wrote: > On 03/24/10 23:28, Juan Quintela wrote: >> Humm, I think it means. Can you migrate from a "new" vga to an old one, >> and maintain it working? > > Depends on the vgabios version. > > vgabios 0.6c will not support vesa gfx modes on older qemu, no matter > whenever you started fresh or migrated to it. > >> - s->vbe_regs[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID0; >> + s->vbe_regs[VBE_DISPI_INDEX_ID] = VBE_DISPI_ID5; >> + s->vbe_regs[VBE_DISPI_INDEX_VIDEO_MEMORY_64K] = s->vram_size / (64 * 1024); > >> After migration, vbe_regs[VBE_DISPI_INDEX_ID] would have the value >> VBE_DISPI_ID5, but vbe_regs[VBE_DISPI_INDEX_VIDEO_MEMORY_64K] will have >> any random value, no? > > vgabios uses both once at init time. Then our big problem is migration between read of the 1st register and of the 2nd register, no? Furthermore, older vga bios, seing VBE_DISPI_ID5, what are they going to do? > resetting vga will reset the vbe > regs too. Yes, but I guess you agree that forcing a reset in the middle of a live migration makes the whole point of migration moot :-) > So when migrating from new to old qemu: Before reset > vgabios will have the video memory size saved somewhere. After reset > ID will reset to ID0, and in case you are running vgabios 0.6c vesa > gfx modes will stop working. I see this part, but I still think that we have a window where we can be in very bad shape, no? I guess that we don't support anything different that vgabios, so .... > cheers, > Gerd