[Xen-devel] [RFC] Disable xen platform device when it is not needed.

[Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>]

I plan to create the patch to disable xen platform device when it
is not needed. Please let me know if anyone has a comment.

Windows guest shows xen platform device as unknown
device with "!" mark in the device manager, when PV drivers are not
loaded. So I'd like to disable xen platform device.

If following conditions are all true, I will disable xen platform
device. Otherwise, xen platform device will be enabled.

    - All entries in "disk" parameter have "ioemu:" prefix in DEV field.
        Example:
        disk = [ '/var/images/guest.img,ioemu:hda,w', ',ioemu:hdc:cdrom,r' ]

    - All entries in "vif" parameter have "type=ioemu".
        Example:
        vif = [ 'type=ioemu, bridge=eth0', 'type=ioemu, bridge=eth1' ]

    - "vscsi" parameter is not specified.

Xen platform device has functions for PV drivers and guest
firmware (hvmloader and rombios). The functions for PV drivers will be
disabled when xen platform device is disabled. This is no problem. But
the function for guest firmware should not be disabled.

I will move the function for guest firmware from xen platform device
to host bridge. The interface between host bridge and guest firmware
will be in PCI configuration space, because host bridge does not have
io resource and memory resource.

The function which I will move is switching RW/RO state of ROM memory
area. Please refer
qemu-xen/hw/xen_platform.c:xen_platform_ioport_writeb. I will not move
the other functions.

Thanks,
--
Yuji Shimada


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