On 03/21/2013 09:26 AM, Michael S. Tsirkin wrote: >>> >>> Thanks. Same place in latest 3.0: >>> A PCI Express Endpoint must not depend on operating system allocation of >>> I/O resources claimed through BAR(s). >>> A PCI Express Endpoint must not generate I/O Requests. >>> of course this only applies to express :) >>> >> >> And it does... but it has implications for the OS resource manager that >> if Linux violates, we need to fix it. We should not fail a device in >> generic code because an I/O BAR allocation fails. The device driver may >> opt to fail the allocation. >> >> (Note that having an I/O BAR is not *generating* an I/O request.) > > Right. So if I read this literally, I should be able to boot > from the device even if it does not have an I/O BAR, > and BIOS really should not assume it has an I/O BAR option, > and if as you suggest it can't use MMIO, what is left? > config cycles. > > So coming back to the issue that started it all, > BIOS will be able to boot without I/O BAR, no good > reasons to have any capabilities pointing at I/O BARs, > so no need for duplicate capabilities? > First of all, you appear to be deliberately overinterpreting -- the BIOS is the resource manager here, so it can obviously make sure the I/O resource is available to the boot device. The performance argument, though, which is the more important one, still remains, so your conclusion is invalid. -hpa _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
