On Fri, Sep 16, 2016 at 09:23:30AM +0200, Laszlo Ersek wrote:
On 09/16/16 08:28, Martin Kletzander wrote:
On Fri, Sep 16, 2016 at 06:04:46AM +0200, Laszlo Ersek wrote:
Most of QEMU's PCI display device models, such as:

 libvirt video/model/@type  QEMU -device
 -------------------------  ------------
 cirrus                     cirrus-vga
 vga                        VGA
 qxl                        qxl-vga
 virtio                     virtio-vga

come with a linear framebuffer (sometimes called "VGA compatibility
framebuffer"). This linear framebuffer lives in one of the PCI device's
MMIO BARs, and allows guest code (primarily: firmware drivers, and
non-accelerated OS drivers) to display graphics with direct memory
access.

Due to architectural reasons on aarch64/KVM hosts, this kind of
framebuffer doesn't / can't work in

 qemu-system-(arm|aarch64) -M virt

machines. Cache coherency issues guarantee a corrupted / unusable
display.
The problem has been researched by several people, including kvm-arm
maintainers, and it's been decided that the best way (practically the
only
way) to have boot time graphics for such guests is to consolidate on
QEMU's "virtio-gpu-pci" device.

From <https://bugzilla.redhat.com/show_bug.cgi?id=1195176>, libvirt
supports

 <devices>
   <video>
     <model type='virtio'/>
   </video>
 </devices>

but libvirt unconditionally maps @type='virtio' to QEMU's "virtio-vga"
device model. (See the qemuBuildDeviceVideoStr() function and the
"qemuDeviceVideo" enum impl.)

According to the above, this is not right for the "virt" machine type;
the
qemu-system-(arm|aarch64) binaries don't even recognize the "virtio-vga"
device model (justifiedly). Whereas "virtio-gpu-pci", which is a pure
virtio device without a compatibility framebuffer, is available, and
works
fine.

(The ArmVirtQemu ("AAVMF") platform of edk2 -- that is, the UEFI firmware
for "virt" -- supports "virtio-gpu-pci", as of upstream commit
3ef3209d3028. See
<https://tianocore.acgmultimedia.com/show_bug.cgi?id=66>.)

Override the default mapping of "virtio", from "virtio-vga" to
"virtio-gpu-pci", if qemuDomainMachineIsVirt() evaluates to true.

Cc: Andrea Bolognani <abolo...@redhat.com>
Cc: Drew Jones <drjo...@redhat.com>
Cc: Marc-André Lureau <marcandre.lur...@redhat.com>
Suggested-by: Marc-André Lureau <marcandre.lur...@redhat.com>
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1372901
Signed-off-by: Laszlo Ersek <ler...@redhat.com>

Very nicely written, makes sense and since virtio-vga didn't work for
virt machines, there is no problem with changing it.

Thank you!

One small nit though, syntax-check will complain that one of the lines
in the .args file is longer, you can either use 'tests/test-wrap-argv.pl
--in-place
tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args'
or just squash this diff in, whatever you find easier:

While working on the test data, I consulted other files, and I noticed
that they were carefully wrapped. I tried to do the same -- did I fail?

$ wc -L \
 tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args
74 tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args

and "tests/test-wrap-argv.pl" has

   my $max_len = 78;

Hmmm... After running the script, it looks like I was too cautious. The
problem is actually that I broke one of those lines too early, and now
it's too short. :)


It's "prefer wrapping where spaces are, then wrap after commas", the
check is done by running the same script that can fix it in place for
you, so I think there is no need for v2 just to check some whitespaces
for which we have a script =D

I'll send a v2.

Thanks!
Laszlo

diff --git
i/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args
w/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args
index 56dbdfb66fa2..76ee977a3ca2 100644
--- i/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args
+++ w/tests/qemuxml2argvdata/qemuxml2argv-aarch64-video-virtio-gpu-pci.args
@@ -20,7 +20,7 @@ QEMU_AUDIO_DRV=none \
addr=0x1 \
-device ioh3420,port=0x9,chassis=2,id=pci.2,bus=pcie.0,multifunction=on,\
addr=0x1.0x1 \
--device virtio-net-pci,vlan=0,id=net0,mac=52:54:00:73:34:53,bus=pci.1,\
-addr=0x0,bootindex=1 \
+-device
virtio-net-pci,vlan=0,id=net0,mac=52:54:00:73:34:53,bus=pci.1,addr=0x0,\
+bootindex=1 \
-net user,vlan=0,name=hostnet0 \
-device virtio-gpu-pci,id=video0,bus=pci.2,addr=0x0
--

Other than that, with that small thing fixed:

Acked-by: Martin Kletzander <mklet...@redhat.com>

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