[PATCH v3 1/2] x86: fsp: Don't program MTRR for DRAM for FSP1

[Bin Meng <bmeng.cn@gmail.com>]

There are several outstanding issues as to why this does not apply
to FSP1:

* For FSP1, the system memory and reserved memory used by FSP are
  already programmed in the MTRR by FSP.
* The 'mtrr_top' mistakenly includes TSEG memory range that has the
  same RES_MEM_RESERVED resource type. Its address is programmed
  and reported by FSP to be near the top of 4 GiB space, which is
  not what we want for SDRAM.
* The call to mtrr_add_request() is not guaranteed to have its size
  to be exactly the power of 2. This causes reserved bits of the
  IA32_MTRR_PHYSMASK register to be written which generates #GP.

For FSP2, it seems this is necessary as without this, U-Boot boot
process on Chromebook Coral goes very slowly.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

---

(no changes since v2)

Changes in v2:
- Keep programing MTRR to FSP2 only

 arch/x86/lib/fsp/fsp_dram.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/fsp/fsp_dram.c b/arch/x86/lib/fsp/fsp_dram.c
index 8ad9aeedac..2bd408d0c5 100644
--- a/arch/x86/lib/fsp/fsp_dram.c
+++ b/arch/x86/lib/fsp/fsp_dram.c
@@ -48,12 +48,28 @@ int dram_init_banksize(void)
 	phys_addr_t mtrr_top;
 	phys_addr_t low_end;
 	uint bank;
+	bool update_mtrr;
+
+	/*
+	 * For FSP1, the system memory and reserved memory used by FSP are
+	 * already programmed in the MTRR by FSP. Also it is observed that
+	 * FSP on Intel Queensbay platform reports the TSEG memory range
+	 * that has the same RES_MEM_RESERVED resource type whose address
+	 * is programmed by FSP to be near the top of 4 GiB space, which is
+	 * not what we want for DRAM.
+	 *
+	 * However it seems FSP2's behavior is different. We need to add the
+	 * DRAM range in MTRR otherwise the boot process goes very slowly,
+	 * which was observed on Chrromebook Coral with FSP2.
+	 */
+	update_mtrr = CONFIG_IS_ENABLED(FSP_VERSION2);
 
 	if (!ll_boot_init()) {
 		gd->bd->bi_dram[0].start = 0;
 		gd->bd->bi_dram[0].size = gd->ram_size;
 
-		mtrr_add_request(MTRR_TYPE_WRBACK, 0, gd->ram_size);
+		if (update_mtrr)
+			mtrr_add_request(MTRR_TYPE_WRBACK, 0, gd->ram_size);
 		return 0;
 	}
 
@@ -76,8 +92,10 @@ int dram_init_banksize(void)
 		} else {
 			gd->bd->bi_dram[bank].start = res_desc->phys_start;
 			gd->bd->bi_dram[bank].size = res_desc->len;
-			mtrr_add_request(MTRR_TYPE_WRBACK, res_desc->phys_start,
-					 res_desc->len);
+			if (update_mtrr)
+				mtrr_add_request(MTRR_TYPE_WRBACK,
+						 res_desc->phys_start,
+						 res_desc->len);
 			log_debug("ram %llx %llx\n",
 				  gd->bd->bi_dram[bank].start,
 				  gd->bd->bi_dram[bank].size);
@@ -92,7 +110,8 @@ int dram_init_banksize(void)
 	 * Set up an MTRR to the top of low, reserved memory. This is necessary
 	 * for graphics to run at full speed in U-Boot.
 	 */
-	mtrr_add_request(MTRR_TYPE_WRBACK, 0, mtrr_top);
+	if (update_mtrr)
+		mtrr_add_request(MTRR_TYPE_WRBACK, 0, mtrr_top);
 
 	return 0;
 }
-- 
2.25.1