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.
>
> 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. So we shouldn't rule it out going forward.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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