fix low bits in ROM and I/O sizing

This cleans up handling of low bits during BAR sizing,
to match PCI spec requirements, and to use symbolic
constants from pci_regs.h

Issues fixed:
For ROM BARs, bit 0 is writeable (enable bit), which we not
only don't want to set, but it will stick and make us think
it's an I/O port resource.
Further, PCI spec defines the following bits as reserved:
- bit 1 in I/O BAR
- bits 10:1 in ROM BAR
and we should be careful and preserve any values there,
and should ignore anything we read from these registers.
Bits 3:2 in I/O BAR might be writeable, so it
is wrong to mask them when calculating BAR size.

Spec references:
See for I/O and memory, and for ROM,
6.1 for reserved bit handling;
pages 225, 228 and 214 in PCI spec revision 3.0.

See also Qemu pcbios commit 6ddb9f5c742b2b82b1755d7ec2a127f6e20e3806

Signed-off-by: Gleb Natapov <>
Signed-off-by: Michael S. Tsirkin <>
1 file changed
tree: af3f52cd95be4a0996f7b770b89bf9bc56fe7b5e
  1. src/
  2. tools/
  3. vgasrc/
  4. .gitignore
  7. Makefile
  9. TODO