intel/fsp2_0: Move temporary RAM to .bss with FSP_USES_CB_STACK

The documentation for StackBase and StackSize in FSPM_ARCH_UPD is
confusing. Previously the region was shared for heap and stack,
starting with FSP2.1 only for heap (or 'temporary RAM') for HOBs.

Moving the allocation outside DCACHE_BSP_STACK_SIZE allows use of
stack guards and reduces amount of reserved CAR for bootblock and
verstage, as the new allocation in .bss is only taken in romstage.

BUG=b:140268415

Change-Id: I4cffcc73a89cb97ab7759dd373196ce9753a6307
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35233
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

2 files changed, 20 insertions, 12 deletions

diff --git a/src/drivers/intel/fsp2_0/Kconfig b/src/drivers/intel/fsp2_0/Kconfig
index 3fb39d5076..541ec47b46 100644
--- a/src/drivers/intel/fsp2_0/Kconfig
+++ b/src/drivers/intel/fsp2_0/Kconfig
@@ -152,6 +152,11 @@ config FSP_USES_CB_STACK
 	  without reinitializing stack pointer. This feature is
 	  supported Icelake onwards.
 
+config FSP_TEMP_RAM_SIZE
+	hex
+	default 0x10000
+	depends on FSP_USES_CB_STACK
+
 config VERIFY_HOBS
 	bool "Verify the FSP hand-off-blocks"
 	default n
diff --git a/src/drivers/intel/fsp2_0/memory_init.c b/src/drivers/intel/fsp2_0/memory_init.c
index 0797c2e3fc..9789c9653a 100644
--- a/src/drivers/intel/fsp2_0/memory_init.c
+++ b/src/drivers/intel/fsp2_0/memory_init.c
@@ -34,6 +34,8 @@
 #include <fsp/memory_init.h>
 #include <types.h>
 
+static uint8_t temp_ram[CONFIG_FSP_TEMP_RAM_SIZE] __aligned(sizeof(uint64_t));
+
 /* TPM MRC hash functionality depends on vboot starting before memory init. */
 _Static_assert(!CONFIG(FSP2_0_USES_TPM_MRC_HASH) ||
 	       CONFIG(VBOOT_STARTS_IN_BOOTBLOCK),
@@ -161,6 +163,7 @@ static enum cb_err check_region_overlap(const struct memranges *ranges,
 
 	return CB_SUCCESS;
 }
+
 static enum cb_err setup_fsp_stack_frame(FSPM_ARCH_UPD *arch_upd,
 		const struct memranges *memmap)
 {
@@ -168,17 +171,6 @@ static enum cb_err setup_fsp_stack_frame(FSPM_ARCH_UPD *arch_upd,
 	uintptr_t stack_end;
 
 	/*
-	 * FSP 2.1 version would use same stack as coreboot instead of
-	 * setting up seprate stack frame. FSP 2.1 would not relocate stack
-	 * top and does not reinitialize stack pointer.
-	 */
-	if (CONFIG(FSP_USES_CB_STACK)) {
-		arch_upd->StackBase = (void *)_car_stack_start;
-		arch_upd->StackSize = CONFIG_DCACHE_BSP_STACK_SIZE;
-		return CB_SUCCESS;
-	}
-
-	/*
 	 * FSPM_UPD passed here is populated with default values
 	 * provided by the blob itself. We let FSPM use top of CAR
 	 * region of the size it requests.
@@ -197,8 +189,19 @@ static enum cb_err fsp_fill_common_arch_params(FSPM_ARCH_UPD *arch_upd,
 					bool s3wake, uint32_t fsp_version,
 					const struct memranges *memmap)
 {
-	if (setup_fsp_stack_frame(arch_upd, memmap))
+	/*
+	 * FSP 2.1 version would use same stack as coreboot instead of
+	 * setting up separate stack frame. FSP 2.1 would not relocate stack
+	 * top and does not reinitialize stack pointer. The parameters passed
+	 * as StackBase and StackSize are actually for temporary RAM and HOBs
+	 * and are not related to FSP stack at all.
+	 */
+	if (CONFIG(FSP_USES_CB_STACK)) {
+		arch_upd->StackBase = temp_ram;
+		arch_upd->StackSize = sizeof(temp_ram);
+	} else if (setup_fsp_stack_frame(arch_upd, memmap)) {
 		return CB_ERR;
+	}
 
 	fsp_fill_mrc_cache(arch_upd, fsp_version);