Re: [SeaBIOS] [PATCH 3/4] move 64bit pci window to end of address space

[Gerd Hoffmann]

On Mon, Nov 21, 2022 at 11:57:35AM +0100, Paul Menzel wrote:
> Dear Gerd,
> 
> 
> Thank you for the patch.
> 
> Am 21.11.22 um 11:32 schrieb Gerd Hoffmann:
> > When the size of the physical address space is known (PhysBits is not
> > zero) move the 64bit pci io window to the end of the address space.
> 
> It’d be great, if you elaborated, why this is an improvement.

It makes seabios follow a common pattern.  real mode address space
has io resources mapped high (below 1M).  32-bit address space has
io resources mapped high too (below 4G).  This does the same for
64-bit resources.

Physical hardware does simliar things, here is my workstation:

    # sudo cat /proc/iomem 
    [ ... regions below 4G snipped ... ]
    100000000-a36ffffff : System RAM
      2e6000000-2e7002607 : Kernel code
      2e7200000-2e7e84fff : Kernel rodata
      2e8000000-2e8326e7f : Kernel data
      2e8b6e000-2e8ffffff : Kernel bss
    a37000000-a37ffffff : RAM buffer
    2000000000-2fffffffff : PCI Bus 0000:00
      2ffff00000-2ffff0ffff : 0000:00:1f.3
      2ffff10000-2ffff1ffff : 0000:00:14.0
        2ffff10000-2ffff1ffff : xhci-hcd
      2ffff20000-2ffff23fff : 0000:00:1f.3
        2ffff20000-2ffff23fff : ICH HD audio
      2ffff24000-2ffff240ff : 0000:00:1f.4
      2ffff25000-2ffff25fff : 0000:00:16.0
        2ffff25000-2ffff25fff : mei_me

There is a larger gap between the end of memory and start of the pci io
window.  It's not the end of the *cpu* physical address space (that
would be 7fffffffff aka phys-bits=39).  Maybe there are additional
constrains in the io chipset (which is a non-issue for virtual
machines).

take care,
  Gerd