[coreboot] [PATCH] v3: Work around broken MTRR setup in VIA CAR

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Sat Nov 1 23:21:24 CET 2008

Once we touch the MTRRs in VIA disable_car(), the CPU resets. Since
workarounds are better than instant reboots, mangle the code so that it
only switches stacks and flushes the cache.

There's also one genuine fix in there: Switch %esp before CAR is
disabled. That way, debugging becomes easier and the stack is always valid.

Many thanks to Corey for testing countless iterations of that code.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006 at gmx.net>
Attached for poor gmail users.

Index: corebootv3-via_car/arch/x86/via/stage1.c
--- corebootv3-via_car/arch/x86/via/stage1.c	(Revision 977)
+++ corebootv3-via_car/arch/x86/via/stage1.c	(Arbeitskopie)
@@ -35,6 +35,7 @@
 void disable_car(void)
+	printk(BIOS_DEBUG, "disable_car entry\n");
 	/* Determine new global variable location. Stack organization from top
 	 * Top 4 bytes are reserved
 	 * Pointer to global variables
@@ -45,16 +46,25 @@
 	const struct global_vars *newlocation = (struct global_vars *)((RAM_STACK_BASE - sizeof(struct global_vars *) - sizeof(struct global_vars)) & ~0x7);
 	/* Copy global variables to new location. */
 	memcpy(newlocation, global_vars(), sizeof(struct global_vars));
+	printk(BIOS_DEBUG, "disable_car global_vars copy done\n");
 	/* Set the new global variable pointer. */
 	*(struct global_vars **)(RAM_STACK_BASE - sizeof(struct global_vars *)) = newlocation;
+	printk(BIOS_DEBUG, "disable_car global_vars pointer adjusted\n")
+	printk(BIOS_DEBUG, "entering asm code now\n");
+#define HALT_AFTER 2
 	__asm__ __volatile__(
+	"	movl	%[newesp], %%esp	\n"
 	/* We don't need cache as ram for now on */
 	/* disable cache */
 	"	movl    %%cr0, %%eax		\n"
 	"	orl    $(0x1<<30),%%eax		\n"
 	"	movl    %%eax, %%cr0		\n"
+	/* The MTRR setup below causes the machine to reset. Must investigate. */
 	/* disable fixed mtrr from now on, it will be enabled by coreboot_ram again*/
 	"	movl    %[_SYSCFG_MSR], %%ecx	\n"
 	"	rdmsr				\n"
@@ -75,10 +85,10 @@
 	"	movl    %%cr0, %%eax		\n"
 	"	andl    $0x9fffffff,%%eax	\n"
 	"	movl    %%eax, %%cr0		\n"
 	"	wbinvd				\n"
-	"	movl	%[newesp], %%esp	\n"
 	"	call stage1_phase3		\n"
 	:: [newesp] "i" (newlocation),


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