From 790baef3b93e0f194bca266f32f620898b84951f Mon Sep 17 00:00:00 2001
From: Simon Glass <sjg@chromium.org>
Date: Sat, 15 Mar 2025 14:25:47 +0000
Subject: [PATCH] x86: emulation: Set an MTRR for the RAM

QEMU likes to have an MTRR set up, just like real machines. Add an MTRR
which covers the total RAM size.

This does nothing on machines without MTRRs.

Signed-off-by: Simon Glass <sjg@chromium.org>
---
 arch/x86/cpu/qemu/dram.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/cpu/qemu/dram.c b/arch/x86/cpu/qemu/dram.c
index 62a301c0fd3..ba3638e6acc 100644
--- a/arch/x86/cpu/qemu/dram.c
+++ b/arch/x86/cpu/qemu/dram.c
@@ -4,7 +4,9 @@
  */
 
 #include <init.h>
+#include <spl.h>
 #include <asm/global_data.h>
+#include <asm/mtrr.h>
 #include <asm/post.h>
 #include <asm/arch/qemu.h>
 #include <linux/sizes.h>
@@ -44,6 +46,22 @@ int dram_init(void)
 	gd->ram_size += qemu_get_high_memory_size();
 	post_code(POST_DRAM);
 
+	if (xpl_phase() == PHASE_BOARD_F) {
+		u64 total = gd->ram_size;
+		int ret;
+
+		if (total > SZ_2G + SZ_1G)
+			total += SZ_1G;
+		ret = mtrr_add_request(MTRR_TYPE_WRBACK, 0, total);
+		if (ret != -ENOSYS) {
+			if (ret)
+				return log_msg_ret("mta", ret);
+			ret = mtrr_commit(false);
+			if (ret)
+				return log_msg_ret("mtc", ret);
+		}
+	}
+
 	return 0;
 }
 
-- 
2.39.5