Re: [Qemu-devel] [BUG] [Seabios] PCI 64bit BARs on Win2008 - unable to start the device. (ACPI lacks the _DSM method)

[Gerd Hoffmann]

On 12/14/11 05:30, Alexey Korolev wrote:
> Hi,
>>>
>>> It shouldn't be that hard to add the latter though.  seabios needs two
>>> more pci_region_type (PCI_REGION_TYPE_MEM_64 and
>>> PCI_REGION_TYPE_PREFMEM_64) to track and map 64bit bars separately.  And
>>> a address space window where it can map 64bit bars to.
>> Right. This is a thing I'm thinking about now. I seems that the
>> specifying 0x0 address in 64bit BARS is a bad idea. At least older
>> versions of Linux just hang as soon as requested range does not fit in
>> first 4GB.
>> So the only option would be specifying the particular address range.
>> It seems this works for everything - yet.
> I wonder if there any particular reason to separate prefetchable a
> non-prefetchable memory regions in pciinit? Extra two more regions would
> make code more complex.

Oh yes, there is.  Which reminds me that the whole thing isn't that easy
unfortunaly ...

The reason are pci bridges.  They have two memory regions, one for
prefetchable and one for non-prefetchable memory.  All devices behind a
pci bridge must have the bars within the bridges memory regions, thats
why they are grouped together.

This also implies that a 32bit and a 64bit bar (of the same type) behind
a pci bridge must be mapped next to each other, so moving up 64bit bars
unconditionally isn't going to fly.  Devices behind bridges need some
extra care, only when all bars are 64bit capable they can actually be
mapped above 4G.

cheers,
  Gerd