From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36672) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZIw5q-0007Kb-AH for qemu-devel@nongnu.org; Sat, 25 Jul 2015 05:50:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZIw5l-0005uh-BZ for qemu-devel@nongnu.org; Sat, 25 Jul 2015 05:50:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55169) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZIw5l-0005pQ-7B for qemu-devel@nongnu.org; Sat, 25 Jul 2015 05:50:05 -0400 Message-ID: <1437817799.15305.22.camel@redhat.com> From: Gerd Hoffmann Date: Sat, 25 Jul 2015 11:49:59 +0200 In-Reply-To: <20150721135122.374f21a9@arm.com> References: <55A158AF.8050907@redhat.com> <1436772752.26533.2.camel@redhat.com> <55A38FBD.4000203@redhat.com> <55AD46A3.6060308@redhat.com> <55AE3628.4010400@suse.de> <20150721135122.374f21a9@arm.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] selecting VIRTIO_INPUT and VIRTIO_VGA List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marc Zyngier Cc: Peter Maydell , Ard Biesheuvel , Alexander Graf , qemu-devel , Paolo Bonzini , Laszlo Ersek Hi, > > I agree. Also, as far as I understood Marc, his hope was that the fix to > > halfway working VGA emulation would be virtio-gpu. Note we have both virtio-vga and virtio-gpu-pci. virtio-vga has vga compatibility built-in, otherwise the two are identical. virtio-gpu-pci is enabled along with all other virtio drivers, so arm + aarch64 have that already. > 2) Use the fact that there is actually hardly any legacy for ARM VMs, > and embrace paravirtualized devices entirely. We do it for disks, > network interfaces. Why not display? Why not input? We have both now (qemu 2.4+, linux 4.1+ for input, linux 4.2+ for gpu). Works just fine on arm (tcg tested). aarch64 not yet (with vanilla upstream linux kernel) due to lack of generic pci host support. > Using VGA makes sense on x86 because this is a standard on that > platform. Every system has one. You can't expect the same thing on ARM > (evil persons would even say that you can't expect anything at all). So > let's take this opportunity to use the best tool for the job. Virtio > fits that bill pretty well apparently. Big question is (a) whenever we need a firmware framebuffer and (b) how to implement that best. virtio-vga/virtio-gpu-pci in paravirt (native) mode requires the guest explicitly request screen updates. There is no dirty page tracking, and guest writes to memory do *not* magically appear on the screen. I don't think implementing a EFI driver for that is going to fly. virtio-vga in vga-compat mode uses a framebuffer with the usual dirty tracking logic in pci bar 0 (simliar to stdvga). Which is exactly the thing causing the cache coherency issues on aarch64 if I understand things correctly. Programming (modesetting) works without legacy vga io ports, you can use the mmio regs in pci bar 1 instead (applies to both virtio-vga and stdvga btw), and QemuVideoDxe actually uses the mmio bar. cheers, Gerd