[coreboot-gerrit] Change in coreboot[master]: nb/intel/sandybridge/raminit: Add comments

[Patrick Rudolph (Code Review)]

Patrick Rudolph has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/40947 )

Change subject: nb/intel/sandybridge/raminit: Add comments
......................................................................

nb/intel/sandybridge/raminit: Add comments

Add comments found when testing ECC scrubbing code.
This is a cosmetic change.

Change-Id: I7975f6070c2002930eec407a6b101a1295495b25
Signed-off-by: Patrick Rudolph 
---
M src/northbridge/intel/sandybridge/raminit_common.c
1 file changed, 8 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/47/40947/1

diff --git a/src/northbridge/intel/sandybridge/raminit_common.c b/src/northbridge/intel/sandybridge/raminit_common.c
index e80abe7..609204e 100644
--- a/src/northbridge/intel/sandybridge/raminit_common.c
+++ b/src/northbridge/intel/sandybridge/raminit_common.c
@@ -298,8 +298,14 @@
    		reg |= (dimmB->width / 8 - 1) << 20;
    	}

-		reg |= 1 << 21; /* Rank interleave */
-		reg |= 1 << 22; /* Enhanced interleave */
+		/*
+		 * Rank interleave: Bit 16 of the physical address space sets
+		 * the rank to use in a dual single rank DIMM configuration.
+		 * That results in every 64KiB being interleaved between two ranks.
+		 */
+		reg |= 1 << 21;
+		/* Enhanced interleave */
+		reg |= 1 << 22;

if ((dimmA && (dimmA->ranks > 0)) || (dimmB && (dimmB->ranks > 0))) {
    		ctrl->mad_dimm[channel] = reg;