[SeaBIOS] [RfC PATCH 0/2] move apci ports

Gerd Hoffmann kraxel at redhat.com
Tue Jan 15 14:57:56 CET 2013

On 01/15/13 00:47, Kevin O'Connor wrote:
> On Mon, Jan 14, 2013 at 01:56:03PM +0100, Gerd Hoffmann wrote:
>>   Hi,
>> Currently the acpi (+smbios) io regions are in the middle of the addres
>> space:  At 0xb000 and 0xb100.  And we start allocating I/O ports at
>> 0xc000.  piix additionally has some magic io ports (for cpu + pci
>> hotplug) between 0xae00 and 0xaffff.
>> For q35 I'd like to move the acpi ports out if the way, so we can start
>> allocating io ports at 0x2000 and use the whole 0x2000 -> 0xffff range.
> Is there a shortage of IO ports on q35 without this change?

Problem is each pci bridge needs a 4k out of 64k io address space (if it
has devices with io ports behind it) because that is the smallest io
window allowed by the pci specs.  So if you build a somewhat larger
virtual machine with pcie ports and pci bridges you quickly run out of
address space if you limit yourself to 16k (0xc000+).

> BTW, this type of change would need to wait until after the next
> release.

Sure, it isn't by intention to get this into 1.7.2.


More information about the SeaBIOS mailing list