src/cpu/x86/mtrr/earlymtrr: Add clear_all_var_mtrr

Picasso does not define the state of variable MTRRs on boot. Add a
helper function to clear all MTRRs.

BUG=b:147042464
TEST=Build trembyle

Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Change-Id: I21b887ce12849a95ddd8f1698028fb6bbfb4a7f6
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40764
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/cpu/x86/mtrr/earlymtrr.c b/src/cpu/x86/mtrr/earlymtrr.c
index 4d14a8de08..e4003591f9 100644
--- a/src/cpu/x86/mtrr/earlymtrr.c
+++ b/src/cpu/x86/mtrr/earlymtrr.c
@@ -42,3 +42,17 @@ void set_var_mtrr(
 	maskm.hi = (1 << (cpu_phys_address_size() - 32)) - 1;
 	wrmsr(MTRR_PHYS_MASK(reg), maskm);
 }
+
+void clear_all_var_mtrr(void)
+{
+	msr_t mtrr = {0, 0};
+	int vcnt;
+	int i;
+
+	vcnt = get_var_mtrr_count();
+
+	for (i = 0; i < vcnt; i++) {
+		wrmsr(MTRR_PHYS_MASK(i), mtrr);
+		wrmsr(MTRR_PHYS_BASE(i), mtrr);
+	}
+}