[coreboot-gerrit] Change in coreboot[master]: arch/x86: Cache the TSEG region at the top of ram

[Subrata Banik (Code Review)]

Hello Kyösti Mälkki,

I'd like you to do a code review. Please visit

https://review.coreboot.org/c/coreboot/+/34995

to review the following change.

Change subject: arch/x86: Cache the TSEG region at the top of ram
......................................................................

arch/x86: Cache the TSEG region at the top of ram

This patch helps to save additional  ~6ms of booting time in
normal and s3 resume on CML-hatch.

Change-Id: I59432c02e04af1b931d77de3f6652b0327ca82bb
Signed-off-by: Kyösti Mälkki 
Signed-off-by: Subrata Banik 
---
M src/arch/x86/postcar_loader.c
1 file changed, 21 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/95/34995/1

diff --git a/src/arch/x86/postcar_loader.c b/src/arch/x86/postcar_loader.c
index bceed6c..408d155 100644
--- a/src/arch/x86/postcar_loader.c
+++ b/src/arch/x86/postcar_loader.c
@@ -20,6 +20,7 @@
 #include <cpu/cpu.h>
 #include <cpu/x86/msr.h>
 #include <cpu/x86/mtrr.h>
+#include <cpu/x86/smm.h>
 #include <program_loading.h>
 #include <rmodule.h>
 #include <romstage_handoff.h>
@@ -149,6 +150,23 @@
    set_var_mtrr(mtrr, base, size, MTRR_TYPE_WRPROT);
 }

+/*
+ * Cache the TSEG region at the top of ram. This region 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.
+ */
+static void enable_tseg_cache(struct postcar_frame *pcf)
+{
+	uintptr_t smm_base;
+	size_t smm_size;
+
+	smm_region(&smm_base, &smm_size);
+	postcar_frame_add_mtrr(pcf, smm_base, smm_size,
+				MTRR_TYPE_WRBACK);
+}
+
 void postcar_frame_setup_top_of_dram_usage(struct postcar_frame *pcf,
    			uintptr_t addr, size_t size, int type)
 {
@@ -159,6 +177,9 @@
     */
    if (!acpi_is_wakeup_s3())
    	enable_top_of_dram_cache(addr, size);
+
+	enable_tseg_cache(pcf);
+
    postcar_frame_add_mtrr(pcf, addr, size, type);
 }