[SeaBIOS] [PATCH v3 1/6] pci: add two-pass pci initialization code

[Gerd Hoffmann]

> Hmm but within a bridge we allocate down to top, right?

Yes.  Just the big mem and prefmem blocks which contain everything are 
allocated top-down, exactly to avoid fragmenting the memory by moving 
stuff as far as possible to the top of the address space, leaving a big 
hole between end of guest ram and start of pci allocations.

Within the memory blocks the bars (and bridge windows) are allocated 
bottom-up, sorted by size, with no alignment holes between the bars.

The memory layout created this way looks like this:

00000000-00000fff : reserved
00001000-0009efff : System RAM
0009f000-0009ffff : reserved
000f0000-000fffff : reserved
00100000-3fffbfff : System RAM
   01000000-01472d32 : Kernel code
   01472d33-01b8872f : Kernel data
   01c7b000-01e438b7 : Kernel bss
3fffc000-3fffffff : reserved

^^^ RAM

fc000000-fdffffff : 0000:00:02.0
fe000000-fe0fffff : PCI Bus 0000:01
fe100000-fe1fffff : PCI Bus 0000:02

^^^ prefetchable memory block

The whole block is aligned-down according to the alignment requirements 
of the largest bar (vga framebuffer in that case).

fe900000-fe9fffff : PCI Bus 0000:01
   fe900000-fe901fff : 0000:01:01.0
     fe900000-fe901fff : sym53c8xx
   fe902000-fe902fff : 0000:01:00.0
     fe902000-fe902fff : ehci_hcd
   fe903000-fe9033ff : 0000:01:01.0
     fe903000-fe9033ff : sym53c8xx
fea00000-feafffff : PCI Bus 0000:02
feb00000-feb0ffff : 0000:00:02.0
feb10000-feb1ffff : 0000:00:03.0
feb20000-feb23fff : 0000:00:08.0
   feb20000-feb23fff : ICH HD audio
feb24000-feb24fff : 0000:00:02.0
feb25000-feb25fff : 0000:00:03.0
   feb25000-feb25fff : virtio-pci
feb26000-feb26fff : 0000:00:10.0
   feb26000-feb26fff : virtio-pci
feb27000-feb27fff : 0000:00:11.0
   feb27000-feb27fff : virtio-pci
feb28000-feb28fff : 0000:00:12.0
   feb28000-feb28fff : virtio-pci

^^^ normal memory block

Also aligned down according to the requirements of the largest bar (pci 
bridge memory window in that case).

fec00000-fec003ff : IOAPIC 0
fed00000-fed003ff : HPET 0
fee00000-fee00fff : Local APIC
feffc000-feffffff : reserved
fffc0000-ffffffff : reserved

The code sizes the bridge windows to be a power of two right now.  That 
could be changed.  It would make the allocation code more complicated 
though and I suspect it wouldn't make the packing much better.  Also we 
want some free address space for the bridges anyway so we can hotplug 
stuff, so rounding up the size to the next power of two doesn't hurt 
much IMHO.

cheers,
   Gerd