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Re: [Qemu-devel] [PATCH] Change virtio-console to PCI_CLASS_SERIAL_OTHER

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] Change virtio-console to PCI_CLASS_SERIAL_OTHER
Date: Wed, 27 May 2009 09:21:11 -0500
User-agent: Thunderbird (X11/20090409)

Mark McLoughlin wrote:
From: Adam Jackson <address@hidden>

We're using PCI_CLASS_DISPLAY_OTHER now, but qemu-kvm.git is using

  "As a PCI_CLASS_DISPLAY_OTHER, it reduces primary display somehow on
   Windows XP (possibly Windows disables acceleration since it fails
   to find a driver)."

While this is valid, many versions of X will get confused by it.
Class major number of 0 gets treated as a possibly prehistoric VGA
device, and then the autoconfig logic gets confused trying to figure
out whether the virtio console or the pv vga device are the real VGA.

We should really set a proper class ID. 0x0780 (serial / other) seems
most appropriate. This shouldn't require any kernel changes, the
modalias for virtio looks like:

  alias:          pci:v00001AF4d*sv*sd*bc*sc*i*

so won't care what the base class or subclass are.

It shows up in the guest as:

  00:05.0 Communication controller: Qumranet, Inc. Virtio console

Signed-off-by: Adam Jackson <address@hidden>
Signed-off-by: Mark McLoughlin <address@hidden>

We need a mechanism to toggle this for both this and virtio-blk. The reason a toggle is needed is so that 0.11 can create the same device model as 0.10.

In principle though, I think both changes are reasonable, we just can't do it unconditionally.


Anthony Liguori

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