Fix multipleVGA cards resource conflict on Windows

If multiple VGA-compatible legacy graphic cards decode the IO range
3B0-3BB, 3C0-3DF and MEM range A00000-BFFFF.
Windows 7 complain a resource conflict, so only one VGA card can
works at the same time.

There is a discussion in coreboot mail list before,
please reference thread: "how to prevent legacy resource conflictwith   multipleVGA cards"
http://www.coreboot.org/pipermail/coreboot/2010-October/061508.html

Linux using VGA Arbiter module(vgaarb) to resolve this resource conflict,
Please see the following linux dmesg log, more information can be found in
Linux source dir Documentation/vgaarbiter.txt.
But it seems that windows don't dealwith this conflict.
~# dmesg | grep -i vgaarb
[    0.774076] vgaarb: device added: PCI:0000:00:01.0,decodes=io+mem,owns=io+mem
[    0.776065] vgaarb: device added: PCI:0000:01:00.0,decodes=io+mem,owns=none,l
[    0.780051] vgaarb: loaded
[    0.784049] vgaarb: bridge control possible 0000:01:00.0
[    0.788050] vgaarb: bridge control possible 0000:00:01.0

For the second legacy graphic device, coreboot already disabled the
IO and MEM decode in function set_vga_bridge_bits().
But it will be enabled again in function pci_set_resource(),
if the second legacy vga-compatible graphic device take any IO/MEM resources.

Following log printed by enable_resources() shows the problem:
...snip...
PCI: 00:00.0 cmd <- 06
PCI: 00:01.0 subsystem <- 1022/1410
PCI: 00:01.0 cmd <- 07                <== The first graphic device
PCI: 00:01.1 subsystem <- 1022/1410
PCI: 00:01.1 cmd <- 02
PCI: 00:02.0 bridge ctrl <- 0003
PCI: 00:02.0 cmd <- 07
...snip...
PCI: 01:00.0 cmd <- 03                <== The second graphic device
PCI: 01:00.1 cmd <- 02
PCI: 02:00.0 cmd <- 02
PCI: 03:00.0 cmd <- 03
done.
...snip...

The IO & MEM decoding on the second vga graphic device should be disabled.
Please reference PCI spec. section 3.10 in detail.
set_vga_bridge_bits() would do this work for us, it did the right thing,
but was put to the wrong place, the setting would be overwritten by
assign_resources() later.

In order to make sure the set_vga_bridge_bits() setting not be
overwritten by others, moving the call of set_vga_bridge_bits()
to the end of dev_configure(), instead of at the beginning.

This patch resolved the dual graphic cards resource conflict in windows7,
multiple vga-compatible graphic cards can work together in windows7.

Signed-off-by: Kerry Sheh <shekairui@gmail.com>
Signed-off-by: Kerry Sheh <kerry.she@amd.com>
Change-Id: I0de5e3761b51e2723d9c1dc0c39fff692e3a779d
Reviewed-on: http://review.coreboot.org/489
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>

diff --git a/src/devices/device.c b/src/devices/device.c
index a2619bf00070db755f83b8870f5806313f6352be..8ad9787431e5c03f60f3a45c5f5da07f34357958 100644 (file)
--- a/src/devices/device.c
+++ b/src/devices/device.c
@@ -932,10 +932,6 @@ void dev_configure(void)
        struct device *root;
        struct device *child;
 
-#if CONFIG_VGA_BRIDGE_SETUP == 1
-       set_vga_bridge_bits();
-#endif
-
        printk(BIOS_INFO, "Allocating resources...\n");
 
        root = &dev_root;
@@ -1028,6 +1024,10 @@ void dev_configure(void)
        printk(BIOS_INFO, "Done setting resources.\n");
        print_resource_tree(root, BIOS_SPEW, "After assigning values.");
 
+#if CONFIG_VGA_BRIDGE_SETUP == 1
+       set_vga_bridge_bits();
+#endif
+
        printk(BIOS_INFO, "Done allocating resources.\n");
 }