seabios: fix low bits in ROM and I/O sizing

Message ID
State New
Headers show

Commit Message

Michael S. Tsirkin Oct. 12, 2009, 2:20 p.m.
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

Original-by: Gleb Natapov <>
Signed-off-by: Michael S. Tsirkin <>


So, here's my latest version, I fixed some TABs versus spaces here.
Gleb, if you want to rewrite it using 0xffffffff, or go back to your
original patch, go ahead. It's not really important, either way.
If you are OK as is, let me know and I will try to get this merged.


diff --git a/src/pciinit.c b/src/pciinit.c
index 7d2ea00..031d2f9 100644
--- a/src/pciinit.c
+++ b/src/pciinit.c
@@ -136,16 +136,23 @@  static void pci_bios_init_device(u16 bdf)
         /* default memory mappings */
         for (i = 0; i < PCI_NUM_REGIONS; i++) {
             int ofs;
-            u32 val, size;
+            u32 val, mask, size;
             if (i == PCI_ROM_SLOT)
                 ofs = PCI_ROM_ADDRESS;
                 ofs = PCI_BASE_ADDRESS_0 + i * 4;
-            pci_config_writel(bdf, ofs, 0xffffffff);
+            val = pci_config_readl(bdf, ofs);
+            if (i == PCI_ROM_SLOT)
+                mask = PCI_ROM_ADDRESS_MASK;
+            else if (val & PCI_BASE_ADDRESS_SPACE_IO)
+                mask = PCI_BASE_ADDRESS_IO_MASK;
+            else
+                mask = PCI_BASE_ADDRESS_MEM_MASK;
+            pci_config_writel(bdf, ofs, val | mask);
             val = pci_config_readl(bdf, ofs);
             if (val != 0) {
-                size = (~(val & ~0xf)) + 1;
+                size = (~(val & mask)) + 1;
                 if (val & PCI_BASE_ADDRESS_SPACE_IO)
                     paddr = &pci_bios_io_addr;
                 else if (size >= 0x04000000)