[coreboot] [PATCH] cache type for BIOS flash memory should be WP-MMIO, not WB-MMIO

Scott Duplichan scott at notabs.org
Thu Feb 10 20:32:31 CET 2011


According to AMD documentation, cache type WP should be used for
execution from flash memory. Coreboot uses WB. While there is no
noticeable performance difference between the two settings, use
of WB can cause a problem for a jtag debugger. The attached
patch changes AMD cache as ram setting for flash execution from
WB to WP.

Signed-off-by: Scott Duplichan <scott at notabs.org>

Index: src/cpu/amd/car/cache_as_ram.inc
===================================================================
--- src/cpu/amd/car/cache_as_ram.inc	(revision 6341)
+++ src/cpu/amd/car/cache_as_ram.inc	(working copy)
@@ -294,11 +294,11 @@
 	xorl	%edx, %edx
 	/*
 	 * IMPORTANT: The two lines below can _not_ be written like this:
-	 *   movl $(REAL_XIP_ROM_BASE | MTRR_TYPE_WRBACK), %eax
+	 *   movl $(REAL_XIP_ROM_BASE | MTRR_TYPE_WRPROT), %eax
 	 * http://www.coreboot.org/pipermail/coreboot/2010-October/060855.html
 	 */
 	movl	$REAL_XIP_ROM_BASE, %eax
-	orl	$MTRR_TYPE_WRBACK, %eax
+	orl	$MTRR_TYPE_WRPROT, %eax
 	wrmsr
 
 	movl	$MTRRphysMask_MSR(1), %ecx
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