AMD K8 fam10-15: Tidy up CAR stack switch

Return to empty stack before making the switch.

Change-Id: I6d6f633933fac5bc08d9542c371715f737fb42cf
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/20574
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>

src/cpu/amd/car/cache_as_ram.inc

@@ -599,21 +599,14 @@ CAR_FAM10_ap_out:
 	call	cache_as_ram_main
 
 	call	post_cache_as_ram
+	movl	%eax, %esp
+
+	call	cache_as_ram_new_stack
 
 	/* We will not go back. */
 
 	post_code(0xaf)		/* Should never see this POST code. */
 
-	.globl cache_as_ram_switch_stack
-
-cache_as_ram_switch_stack:
-	/* Return address.  */
-	popl	%eax
-	/* New stack.  */
-	popl	%eax
-	movl	%eax, %esp
-	call	cache_as_ram_new_stack
-
 all_mtrr_msrs:
 	/* fixed MTRR MSRs */
 	.long	MTRR_FIX_64K_00000

src/cpu/amd/car/post_cache_as_ram.c

@@ -125,7 +125,7 @@ static void vErrata343(void)
 	wrmsr(BU_CFG2_MSR, msr);
 }
 
-void post_cache_as_ram(void)
+asmlinkage void * post_cache_as_ram(void)
 {
 	uint32_t family = amd_fam1x_cpu_family();
 
@@ -171,12 +171,10 @@ void post_cache_as_ram(void)
 
 	/* New stack grows right below migrated_car. */
 	print_car_debug("Switching to use RAM as stack...");
-	cache_as_ram_switch_stack(migrated_car);
-
-	/* We do not come back. */
+	return migrated_car;
 }
 
-void cache_as_ram_new_stack(void)
+asmlinkage void cache_as_ram_new_stack(void)
 {
 	print_car_debug("Disabling cache as RAM now\n");
 	disable_cache_as_ram_real(0);	// inline

src/include/cpu/amd/car.h

@@ -4,10 +4,8 @@
 #include <arch/cpu.h>
 
 void cache_as_ram_main(unsigned long bist, unsigned long cpu_init_detectedx);
-void post_cache_as_ram(void);
-
-void cache_as_ram_switch_stack(void *stacktop);
-void cache_as_ram_new_stack(void);
+asmlinkage void * post_cache_as_ram(void);
+asmlinkage void cache_as_ram_new_stack(void);
 
 void disable_cache_as_ram(void);