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

[Anthony Liguori <aliguori@us.ibm.com>]

Mark McLoughlin wrote:
> From: Adam Jackson <ajax@redhat.com>
>
> We're using PCI_CLASS_DISPLAY_OTHER now, but qemu-kvm.git is using
> PCI_CLASS_OTHERS because:
>
>   "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 <ajax@redhat.com>
> Signed-off-by: Mark McLoughlin <markmc@redhat.com>
>   

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.

Regards,

Anthony Liguori