cpu/intel: Refactor platform_enter_postcar()

There are benefits in placing the postcar_frame structure
in .bss and returning control to romstage_main().

Change-Id: I0418a2abc74f749203c587b2763c5f8a5960e4f9
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34808
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

14 files changed, 93 insertions, 165 deletions

diff --git a/src/cpu/intel/car/romstage.c b/src/cpu/intel/car/romstage.c
index 89052d6be6..f6b62192f1 100644
--- a/src/cpu/intel/car/romstage.c
+++ b/src/cpu/intel/car/romstage.c
@@ -22,6 +22,21 @@
 
 #define DCACHE_RAM_ROMSTAGE_STACK_SIZE 0x2000
 
+static struct postcar_frame early_mtrrs;
+
+/* prepare_and_run_postcar() determines the stack to use after
+ * cache-as-ram is torn down as well as the MTRR settings to use. */
+static void prepare_and_run_postcar(struct postcar_frame *pcf)
+{
+	if (postcar_frame_init(pcf, 0))
+		die("Unable to initialize postcar frame.\n");
+
+	fill_postcar_frame(pcf);
+
+	run_postcar_phase(pcf);
+	/* We do not return here. */
+}
+
 static void romstage_main(unsigned long bist)
 {
 	int i;
@@ -52,7 +67,8 @@ static void romstage_main(unsigned long bist)
 		printk(BIOS_DEBUG, "Smashed stack detected in romstage!\n");
 	}
 
-	platform_enter_postcar();
+	prepare_and_run_postcar(&early_mtrrs);
+	/* We do not return here. */
 }
 
 #if !CONFIG(C_ENVIRONMENT_BOOTBLOCK)
diff --git a/src/drivers/intel/fsp1_1/car.c b/src/drivers/intel/fsp1_1/car.c
index 1b6f62c351..f6e42d7bfa 100644
--- a/src/drivers/intel/fsp1_1/car.c
+++ b/src/drivers/intel/fsp1_1/car.c
@@ -24,30 +24,23 @@
 #include <fsp/util.h>
 #include <program_loading.h>
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_mtrr(&pcf, CACHE_ROM_BASE, CACHE_ROM_SIZE,
+	postcar_frame_add_mtrr(pcf, CACHE_ROM_BASE, CACHE_ROM_SIZE,
 			       MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache at least 8 MiB below the top of ram, and at most 8 MiB
 	 * above top of the ram. This satisfies MTRR alignment requirement
 	 * with different TSEG size configurations. */
 	top_of_ram = ALIGN_DOWN((uintptr_t)cbmem_top(), 8*MiB);
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 16*MiB, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 16*MiB, MTRR_TYPE_WRBACK);
 
-	run_postcar_phase(&pcf);
 }
 
 /* This is the romstage entry called from cpu/intel/car/romstage.c */
diff --git a/src/include/cpu/intel/romstage.h b/src/include/cpu/intel/romstage.h
index 47cd169e6a..328f464ec4 100644
--- a/src/include/cpu/intel/romstage.h
+++ b/src/include/cpu/intel/romstage.h
@@ -5,6 +5,10 @@
 
 void mainboard_romstage_entry(unsigned long bist);
 
-void platform_enter_postcar(void);
+/* fill_postcar_frame() is called after raminit completes and right before
+ * calling run_postcar_phase(). Implementation should call postcar_frame_add_mtrr()
+ * to tag memory ranges as cacheable to speed up execution of postcar and
+ * early ramstage. */
+void fill_postcar_frame(struct postcar_frame *pcf);
 
 #endif /* _CPU_INTEL_ROMSTAGE_H */
diff --git a/src/northbridge/intel/e7505/memmap.c b/src/northbridge/intel/e7505/memmap.c
index b954c6af74..c3b59e9415 100644
--- a/src/northbridge/intel/e7505/memmap.c
+++ b/src/northbridge/intel/e7505/memmap.c
@@ -43,17 +43,10 @@ void northbridge_write_smram(u8 smram)
 	pci_write_config8(mch, SMRAMC, smram);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
-
 	/*
 	 * Choose to NOT set ROM as WP cacheable here.
 	 * Timestamps indicate the CPU this northbridge code is
@@ -62,14 +55,10 @@ void platform_enter_postcar(void)
 	 */
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache CBMEM region as WB. */
 	top_of_ram = (uintptr_t)cbmem_top();
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB,
 		MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
 }
diff --git a/src/northbridge/intel/gm45/memmap.c b/src/northbridge/intel/gm45/memmap.c
index 6795f7a61f..9337470e1e 100644
--- a/src/northbridge/intel/gm45/memmap.c
+++ b/src/northbridge/intel/gm45/memmap.c
@@ -134,33 +134,24 @@ void stage_cache_external_region(void **base, size_t *size)
 		+ northbridge_get_tseg_size() - CONFIG_SMM_RESERVED_SIZE);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache 8 MiB region below the top of ram and 2 MiB above top of
 	 * ram to cover both cbmem as the TSEG region.
 	 */
 	top_of_ram = (uintptr_t)cbmem_top();
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB,
 			       MTRR_TYPE_WRBACK);
-	postcar_frame_add_mtrr(&pcf, northbridge_get_tseg_base(),
+	postcar_frame_add_mtrr(pcf, northbridge_get_tseg_base(),
 			       northbridge_get_tseg_size(), MTRR_TYPE_WRBACK);
 
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
 }
diff --git a/src/northbridge/intel/haswell/memmap.c b/src/northbridge/intel/haswell/memmap.c
index 14b66a0fc7..13881e99b2 100644
--- a/src/northbridge/intel/haswell/memmap.c
+++ b/src/northbridge/intel/haswell/memmap.c
@@ -53,29 +53,21 @@ void stage_cache_external_region(void **base, size_t *size)
 	*base = (void *)((uint32_t)cbmem_top() + RESERVED_SMM_OFFSET);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache at least 8 MiB below the top of ram, and at most 8 MiB
 	 * above top of the ram. This satisfies MTRR alignment requirement
 	 * with different TSEG size configurations.
 	 */
 	top_of_ram = ALIGN_DOWN((uintptr_t)cbmem_top(), 8*MiB);
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 16*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 16*MiB,
 			MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
 }
diff --git a/src/northbridge/intel/i440bx/memmap.c b/src/northbridge/intel/i440bx/memmap.c
index 495ca8682a..084679ff4a 100644
--- a/src/northbridge/intel/i440bx/memmap.c
+++ b/src/northbridge/intel/i440bx/memmap.c
@@ -68,27 +68,20 @@ void *cbmem_top(void)
 	return (void *)tom;
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache CBMEM region as WB. */
 	top_of_ram = (uintptr_t)cbmem_top();
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB,
 		MTRR_TYPE_WRBACK);
 
-	run_postcar_phase(&pcf);
 }
diff --git a/src/northbridge/intel/i945/memmap.c b/src/northbridge/intel/i945/memmap.c
index ac1499e0fc..5f3e2569fb 100644
--- a/src/northbridge/intel/i945/memmap.c
+++ b/src/northbridge/intel/i945/memmap.c
@@ -100,33 +100,24 @@ void stage_cache_external_region(void **base, size_t *size)
 		+ northbridge_get_tseg_size() - CONFIG_SMM_RESERVED_SIZE);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache 8 MiB region below the top of ram and 2 MiB above top of
 	 * ram to cover both cbmem as the TSEG region.
 	 */
 	top_of_ram = (uintptr_t)cbmem_top();
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB,
 			MTRR_TYPE_WRBACK);
-	postcar_frame_add_mtrr(&pcf, northbridge_get_tseg_base(),
+	postcar_frame_add_mtrr(pcf, northbridge_get_tseg_base(),
 			       northbridge_get_tseg_size(), MTRR_TYPE_WRBACK);
 
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
 }
diff --git a/src/northbridge/intel/nehalem/memmap.c b/src/northbridge/intel/nehalem/memmap.c
index ec036c9d7c..1a3a6d7cdf 100644
--- a/src/northbridge/intel/nehalem/memmap.c
+++ b/src/northbridge/intel/nehalem/memmap.c
@@ -58,32 +58,22 @@ void stage_cache_external_region(void **base, size_t *size)
 			northbridge_get_tseg_size() - CONFIG_SMM_RESERVED_SIZE);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache at least 8 MiB below the top of ram, and at most 8 MiB
 	 * above top of the ram. This satisfies MTRR alignment requirement
 	 * with different TSEG size configurations.
 	 */
 	top_of_ram = ALIGN_DOWN((uintptr_t)cbmem_top(), 8*MiB);
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB, MTRR_TYPE_WRBACK);
-	postcar_frame_add_mtrr(&pcf, top_of_ram, 8*MiB, MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, top_of_ram, 8*MiB, MTRR_TYPE_WRBACK);
 }
diff --git a/src/northbridge/intel/pineview/memmap.c b/src/northbridge/intel/pineview/memmap.c
index 2f3ff6e921..66900af2ef 100644
--- a/src/northbridge/intel/pineview/memmap.c
+++ b/src/northbridge/intel/pineview/memmap.c
@@ -150,33 +150,23 @@ void stage_cache_external_region(void **base, size_t *size)
 		+ northbridge_get_tseg_size() - CONFIG_SMM_RESERVED_SIZE);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache 8 MiB region below the top of ram and 2 MiB above top of
 	 * ram to cover both cbmem as the TSEG region.
 	 */
 	top_of_ram = (uintptr_t)cbmem_top();
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB,
 			MTRR_TYPE_WRBACK);
-	postcar_frame_add_mtrr(&pcf, northbridge_get_tseg_base(),
+	postcar_frame_add_mtrr(pcf, northbridge_get_tseg_base(),
 			       northbridge_get_tseg_size(), MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
 }
diff --git a/src/northbridge/intel/sandybridge/memmap.c b/src/northbridge/intel/sandybridge/memmap.c
index 7d5c173829..99f11a0f2a 100644
--- a/src/northbridge/intel/sandybridge/memmap.c
+++ b/src/northbridge/intel/sandybridge/memmap.c
@@ -57,38 +57,28 @@ void stage_cache_external_region(void **base, size_t *size)
 			- CONFIG_IED_REGION_SIZE - CONFIG_SMM_RESERVED_SIZE);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	top_of_ram = (uintptr_t)cbmem_top();
 	/* Cache 8MiB below the top of ram. On sandybridge systems the top of
 	 * ram under 4GiB is the start of the TSEG region. It is required to
 	 * be 8MiB aligned. Set this area as cacheable so it can be used later
 	 * for ramstage before setting up the entire RAM as cacheable. */
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB, MTRR_TYPE_WRBACK);
 
 	/* Cache 8MiB at the top of ram. Top of ram on sandybridge systems
 	 * is where the TSEG region resides. However, it is not restricted
 	 * to SMM mode until SMM has been relocated. By setting the region
 	 * to cacheable it provides faster access when relocating the SMM
 	 * handler as well as using the TSEG region for other purposes. */
-	postcar_frame_add_mtrr(&pcf, top_of_ram, 8*MiB, MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
+	postcar_frame_add_mtrr(pcf, top_of_ram, 8*MiB, MTRR_TYPE_WRBACK);
 }
diff --git a/src/northbridge/intel/x4x/memmap.c b/src/northbridge/intel/x4x/memmap.c
index dda838760d..254ca880fa 100644
--- a/src/northbridge/intel/x4x/memmap.c
+++ b/src/northbridge/intel/x4x/memmap.c
@@ -145,33 +145,23 @@ void stage_cache_external_region(void **base, size_t *size)
 		+ northbridge_get_tseg_size() - CONFIG_SMM_RESERVED_SIZE);
 }
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache 8 MiB region below the top of ram and 2 MiB above top of
 	 * ram to cover both cbmem as the TSEG region.
 	 */
 	top_of_ram = (uintptr_t)cbmem_top();
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 8*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 8*MiB,
 			MTRR_TYPE_WRBACK);
-	postcar_frame_add_mtrr(&pcf, northbridge_get_tseg_base(),
+	postcar_frame_add_mtrr(pcf, northbridge_get_tseg_base(),
 			       northbridge_get_tseg_size(), MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
-
-	/* We do not return here. */
 }
diff --git a/src/soc/intel/baytrail/romstage/romstage.c b/src/soc/intel/baytrail/romstage/romstage.c
index 7e2bb64ba6..acdf2613fa 100644
--- a/src/soc/intel/baytrail/romstage/romstage.c
+++ b/src/soc/intel/baytrail/romstage/romstage.c
@@ -49,7 +49,22 @@
  * Because we can't use global variables the stack is used for allocations --
  * thus the need to call back and forth. */
 
-static void platform_enter_postcar(void);
+static struct postcar_frame early_mtrrs;
+
+static void fill_postcar_frame(struct postcar_frame *pcf);
+
+/* prepare_and_run_postcar() determines the stack to use after
+ * cache-as-ram is torn down as well as the MTRR settings to use. */
+static void prepare_and_run_postcar(struct postcar_frame *pcf)
+{
+	if (postcar_frame_init(pcf, 0))
+		die("Unable to initialize postcar frame.\n");
+
+	fill_postcar_frame(pcf);
+
+	run_postcar_phase(pcf);
+	/* We do not return here. */
+}
 
 static void program_base_addresses(void)
 {
@@ -129,9 +144,8 @@ static void romstage_main(uint64_t tsc, uint32_t bist)
 	/* Call into mainboard. */
 	mainboard_romstage_entry(&rp);
 
-	platform_enter_postcar();
-
-	/* We don't return here */
+	prepare_and_run_postcar(&early_mtrrs);
+	/* We do not return here. */
 }
 
 /* This wrapper enables easy transition towards C_ENVIRONMENT_BOOTBLOCK,
@@ -238,28 +252,21 @@ void romstage_common(struct romstage_params *params)
 	romstage_handoff_init(prev_sleep_state == ACPI_S3);
 }
 
-/* setup_stack_and_mtrrs() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use. */
-static void platform_enter_postcar(void)
+static void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache at least 8 MiB below the top of ram, and at most 8 MiB
 	 * above top of the ram. This satisfies MTRR alignment requirement
 	 * with different TSEG size configurations.
 	 */
 	top_of_ram = ALIGN_DOWN((uintptr_t)cbmem_top(), 8*MiB);
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 16*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 16*MiB,
 			       MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
 }
diff --git a/src/soc/intel/broadwell/romstage/romstage.c b/src/soc/intel/broadwell/romstage/romstage.c
index 9c86809368..ca478f7313 100644
--- a/src/soc/intel/broadwell/romstage/romstage.c
+++ b/src/soc/intel/broadwell/romstage/romstage.c
@@ -35,31 +35,23 @@
 #include <soc/romstage.h>
 #include <soc/spi.h>
 
-/* platform_enter_postcar() determines the stack to use after
- * cache-as-ram is torn down as well as the MTRR settings to use,
- * and continues execution in postcar stage. */
-void platform_enter_postcar(void)
+void fill_postcar_frame(struct postcar_frame *pcf)
 {
-	struct postcar_frame pcf;
 	uintptr_t top_of_ram;
 
-	if (postcar_frame_init(&pcf, 0))
-		die("Unable to initialize postcar frame.\n");
 	/* Cache the ROM as WP just below 4GiB. */
-	postcar_frame_add_romcache(&pcf, MTRR_TYPE_WRPROT);
+	postcar_frame_add_romcache(pcf, MTRR_TYPE_WRPROT);
 
 	/* Cache RAM as WB from 0 -> CACHE_TMP_RAMTOP. */
-	postcar_frame_add_mtrr(&pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
+	postcar_frame_add_mtrr(pcf, 0, CACHE_TMP_RAMTOP, MTRR_TYPE_WRBACK);
 
 	/* Cache at least 8 MiB below the top of ram, and at most 8 MiB
 	 * above top of the ram. This satisfies MTRR alignment requirement
 	 * with different TSEG size configurations.
 	 */
 	top_of_ram = ALIGN_DOWN((uintptr_t)cbmem_top(), 8*MiB);
-	postcar_frame_add_mtrr(&pcf, top_of_ram - 8*MiB, 16*MiB,
+	postcar_frame_add_mtrr(pcf, top_of_ram - 8*MiB, 16*MiB,
 			MTRR_TYPE_WRBACK);
-
-	run_postcar_phase(&pcf);
 }
 
 /* Entry from cpu/intel/car/romstage.c. */