Peter Maydell <peter.mayd...@linaro.org> writes: > On 8 July 2013 14:45, Alexander Graf <ag...@suse.de> wrote: >> On 08.07.2013, at 15:23, Peter Maydell wrote: >>> Now I'm completely confused. Why would assigned devices >>> have anything to do with this? Can you explain in more >>> detail, because I don't really see what you're suggesting? >> >> The only missing link we have to create any device using -device >> on the command line is the IRQ line enumeration. If we can allocate >> IRQ lines automatically, we can put any command line given -device >> onto our main system bus that is non-pci, non-isa. > > If the user is expected to be able to get the MMIO address > right (which they'd have to specify on the command line > somehow too) why not require them to specify the IRQ number > while they're doing it? I'm a bit suspicious of anything > that requires the user to specify to that level of detail > though, since it requires a lot of inside knowledge about the > board. > > This is the whole reason for having the separate transport: > the board gets to take care of the board specific detail of > how to wire up the transport, and the user just asks to > create the backends that plug automatically into it. > The virtio command line options are complicated and confusing > enough as it is. > >> So if we want to ever support VFIO for platform devices, >> the user will want to pass -device vfio-ahci,foo=bar on >> the command line to assign an AHCI device. > > This appears to be seriously short on actually specifying > enough information to wire a device up. > >> The only infrastructure blocker we have for that today >> is the IRQ allocation. > > DMA lines? Specifying the right location in the address space? > >> Maybe we could even try to be as smart as putting the MMIO >> regions into guest address space intelligently automatically. > > This sounds likely to cause problems with migration unless > we can guarantee that we always pick the same place.
I think we're trying to fit a square peg into a round hole. virtio-mmio is a virtio transport where each device has a dedicated set of system resources. Alex, it sounds like you want virtio-mmio-bus which would be a single set of system resources that implemented a virtio bus on top of it. Regards, Anthony Liguori > > -- PMM
