nb/intel/x4x/raminit: Fix programming dual channel registers

Some things in programming registers related to dual channel
interleaved operation were wrong.

This also adds some code that could in the future be used when me is
active and claims some memory for its UMA.

This also uses some more sensible variable names to clarify at least
some of the magic.

This fixes memtest86+ failing with some assymetric DIMM configuration.

TESTED on DG43GT: memtest86+ now succeeds on many more different DIMM
configuration setups (would instantly fail at addresses above 4G on
many configurations).

Change-Id: If84099d27100e57437bf214dc4cf975f67c2ea1f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/22914
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

1 files changed, 59 insertions, 27 deletions

diff --git a/src/northbridge/intel/x4x/raminit_ddr2.c b/src/northbridge/intel/x4x/raminit_ddr2.c
index ddbcd5b7009b..6ee34adfc7a3 100644
--- a/src/northbridge/intel/x4x/raminit_ddr2.c
+++ b/src/northbridge/intel/x4x/raminit_ddr2.c
@@ -1157,8 +1157,8 @@ static void dradrb_ddr2(struct sysinfo *s)
 	u32 dra0;
 	u32 dra1;
 	u16 totalmemorymb;
-	u32 size, offset;
-	u32 size0, size1;
+	u32 dual_channel_size, single_channel_size, single_channel_offset;
+	u32 size_ch0, size_ch1, size_me;
 	u8 dratab[2][2][2][4] = {
 	{
 		{
@@ -1245,47 +1245,79 @@ static void dradrb_ddr2(struct sysinfo *s)
 		s->channel_capacity[0], s->channel_capacity[1], totalmemorymb);
 
 	/* Populated channel sizes in MiB */
-	size0 = s->channel_capacity[0];
-	size1 = s->channel_capacity[1];
+	size_ch0 = s->channel_capacity[0];
+	size_ch1 = s->channel_capacity[1];
+	size_me = ME_UMA_SIZEMB;
 
 	MCHBAR8(0x111) = MCHBAR8(0x111) & ~0x2;
 	MCHBAR8(0x111) = MCHBAR8(0x111) | (1 << 4);
 
-	/* Set ME UMA size in MiB */
-	MCHBAR16(0x100) = ME_UMA_SIZEMB;
-
-	/* Set ME UMA Present bit */
-	MCHBAR32(0x111) = MCHBAR32(0x111) | 1;
-
-	size = MIN(size0 - ME_UMA_SIZEMB, size1) * 2;
-
-	MCHBAR16(0x104) = size;
-	MCHBAR16(0x102) = size0 + size1 - size;
+	if (size_me == 0) {
+		dual_channel_size = MIN(size_ch0, size_ch1) * 2;
+	} else {
+		if (size_ch0 == 0) {
+			/* ME needs ram on CH0 */
+			size_me = 0;
+			/* TOTEST: bailout? */
+		} else {
+			/* Set ME UMA size in MiB */
+			MCHBAR16(0x100) = size_me;
+			/* Set ME UMA Present bit */
+			MCHBAR32(0x111) = MCHBAR32(0x111) | 1;
+		}
+		dual_channel_size = MIN(size_ch0 - size_me, size_ch1) * 2;
+	}
+	MCHBAR16(0x104) = dual_channel_size;
+	single_channel_size = size_ch0 + size_ch1 - dual_channel_size;
+	MCHBAR16(0x102) = single_channel_size;
 
 	map = 0;
-	if (size0 == 0)
+	if (size_ch0 == 0)
 		map = 0;
-	else if (size1 == 0)
+	else if (size_ch1 == 0)
 		map |= 0x20;
 	else
 		map |= 0x40;
 
-	if (size == 0)
+	if (dual_channel_size == 0)
 		map |= 0x18;
+	/* Enable flex mode, we hardcode this everywhere */
+	if (size_me == 0) {
+		map |= 0x04;
+		if (size_ch0 <= size_ch1)
+			map |= 0x01;
+	} else {
+		if (size_ch0 - size_me < size_ch1)
+			map |= 0x04;
+	}
 
-	if (size0 - ME_UMA_SIZEMB >= size1)
-		map |= 0x4;
 	MCHBAR8(0x110) = map;
 	MCHBAR16(0x10e) = 0;
 
-	if (size1 != 0)
-		offset = 0;
-	else if ((size0 > size1) && ((map & 0x7) == 0x4))
-		offset = size/2 + (size0 + size1 - size);
-	else
-		offset = size/2 + ME_UMA_SIZEMB;
-	MCHBAR16(0x108) = offset;
-	MCHBAR16(0x10a) = size/2;
+	/*
+	 * "108h[15:0] Single Channel Offset for Ch0"
+	 * This is the 'limit' of the part on CH0 that cannot be matched
+	 * with memory on CH1. MCHBAR16(0x10a) is where the dual channel
+	 * memory on ch0s end and MCHBAR16(0x108) is the limit of the single
+	 * channel size on ch0.
+	 */
+	if (size_me == 0) {
+		if (size_ch0 > size_ch1)
+			single_channel_offset = dual_channel_size / 2
+				+ single_channel_size;
+		else
+			single_channel_offset = dual_channel_size / 2;
+	} else {
+		if ((size_ch0 > size_ch1) && ((map & 0x7) == 4))
+			single_channel_offset = dual_channel_size / 2
+				+ single_channel_size;
+		else
+			single_channel_offset = dual_channel_size / 2
+				+ size_me;
+	}
+
+	MCHBAR16(0x108) = single_channel_offset;
+	MCHBAR16(0x10a) = dual_channel_size / 2;
 }
 
 static void mmap_ddr2(struct sysinfo *s)