On Thu, Mar 21, 2013 at 08:26:52AM -0700, H. Peter Anvin wrote: > On 03/21/2013 08:19 AM, Michael S. Tsirkin wrote: > >> > >> In BIOS (e.g. SeaBIOS), using MMIO is very difficult, so your boot ROM > >> probably wants to use I/O space even if MMIO is available. > > > > Is this a real concern? Modern cards seem to supply PXE ROMs even > > though they have no IO BARs. > > > > Most of them do really ugly hacks in hardware (like putting in a "back > door" in config space) to make that possible. config space register that let us access registers within BAR actually sounds pretty reasonable. Way better than an I/O BAR. > > > > Problem is, BIOS and OS normally assume failure to allocate > > any resources means card won't function and disable it. > > So it does not seem to be worth it to have such a > > device specific failover ability. > > > > That is a violation of the PCIe spec; the PCIe spec specifically states > that failure to allocate an I/O BAR should still allow the device to > function. Where does it say this? Also, if as you say BIOS is not prepared to handle MMIO, and the device is needed for boot, where does this leave us? > So we shouldn't rule it out going forward. > > -hpa I'm not against this as such I just think we need some other solution for BIOS. > -- > H. Peter Anvin, Intel Open Source Technology Center > I work for Intel. I don't speak on their behalf. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
