On 06/05/2013 02:50 PM, Anthony Liguori wrote: > "H. Peter Anvin" <hpa@xxxxxxxxx> writes: > >> On 06/05/2013 09:20 AM, Michael S. Tsirkin wrote: >>> >>> Spec says IO and memory can be enabled/disabled, separately. >>> PCI Express spec says devices should work without IO. >>> >> >> For "native endpoints". Currently virtio would be a "legacy endpoint" >> which is quite correct -- it is compatible with a legacy interface. > > Do legacy endpoints also use 4k for BARs? There are no 4K BARs. In fact, I/O BARs are restricted by spec (there is no technical enforcement, however) to 256 bytes. The 4K come from the upstream bridge windows, which are only 4K granular (historic stuff from when bridges were assumed rare.) However, there can be multiple devices, functions, and BARs inside that window. The issue with PCIe is that each PCIe port is a bridge, so in reality there is only one real device per bus number. > If not, can't we use a new device id for native endpoints and call it a > day? Legacy endpoints would continue using the existing BAR layout. Definitely an option. However, we want to be able to boot from native devices, too, so having an I/O BAR (which would not be used by the OS driver) should still at the very least be an option. -hpa -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
