intel/gm45: Use MMCONF_SUPPORT_DEFAULT

Change all PCI configuration accesses to MMIO for all boards
with gm45 chipset. To enable MMIO style access, add explicit
PCI IO config write in the bootblock.

Change-Id: Id1c839b7d669946e0ca8b6837e5152ebcb9cd334
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/3600
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/northbridge/intel/gm45/bootblock.c

@@ -0,0 +1,27 @@
+#include <arch/io.h>
+
+/* Just re-define these instead of including gm45.h. It blows up romcc. */
+#define D0F0_PCIEXBAR_LO 0x60
+#define D0F0_PCIEXBAR_HI 0x64
+
+static void bootblock_northbridge_init(void)
+{
+	uint32_t reg;
+
+	/*
+	 * The "io" variant of the config access is explicitly used to
+	 * setup the PCIEXBAR because CONFIG_MMCONF_SUPPORT_DEFAULT is set to
+	 * to true. That way all subsequent non-explicit config accesses use
+	 * MCFG. This code also assumes that bootblock_northbridge_init() is
+	 * the first thing called in the non-asm boot block code. The final
+	 * assumption is that no assembly code is using the
+	 * CONFIG_MMCONF_SUPPORT_DEFAULT option to do PCI config acceses.
+	 *
+	 * The PCIEXBAR is assumed to live in the memory mapped IO space under
+	 * 4GiB.
+	 */
+	reg = 0;
+	pci_io_write_config32(PCI_DEV(0,0,0), D0F0_PCIEXBAR_HI, reg);
+	reg = CONFIG_MMCONF_BASE_ADDRESS | (2 << 1) | 1; /* 64MiB - 0-63 buses. */
+	pci_io_write_config32(PCI_DEV(0,0,0), D0F0_PCIEXBAR_LO, reg);
+}