On 08/03/2010 02:24 PM, Avi Kivity wrote:
On 08/03/2010 10:15 PM, Anthony Liguori wrote:
fw_cfg has to be available pretty early on so relying on a PCI device
isn't reasonable. Having dual interfaces seems wasteful.
Agree.
We're already doing bulk data transfer over fw_cfg as we need to do
it to transfer roms and potentially a boot splash.
Why do we need to transfer roms? These are devices on the memory bus
or pci bus, it just needs to be there at the right address.
Not quite. The BIOS owns the option ROM space. The way it works on
bare metal is that the PCI ROM BAR gets mapped to some location in
physical memory by the BIOS, the BIOS executes the initialization
vector, and after initialization, the ROM will reorganize itself into
something smaller. It's nice and clean.
But ISA is not nearly as clean. Ultimately, to make this mix work in a
reasonable way, we have to provide a side channel interface to SeaBIOS
such that we can deliver ROMs outside of PCI and still let SeaBIOS
decide how ROMs get organized.
It's additionally complicated by the fact that we didn't support PCI ROM
BAR until recently so to maintain compatibility with -M older, we have
to use a side channel to lay out option roms.
Regards,
Anthony Liguori
Boot splash should just be another rom as it would be on a real system.
Even outside of loading an initrd, the performance is going to start
to matter with a large number of devices.
I don't really see why.
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