From Keith Hui:

This patch implements a full SDRAM buffer strength programming algorithm in
set_dram_buffer_strength(), checked against my P2B-LS factory BIOS. With this
in place, I now have 133MHz (!) stability with three 256MB PC133 modules, and
can boot Fedora 11 all the way to the init daemon (actually upstart, but that's
another story). Not to login prompt yet. We'll find out why later.

This again assumes a 4-DIMM board because that's all I have. I need someone
with a 3-DIMM board to test it.

As a bonus, there's a big comment block within that illustrates the algorithm.
:-)

Signed-off-by: Keith Hui <buurin@gmail.com>
Acked-by: Stefan Reinauer <stepan@coresystems.de>




git-svn-id: svn://svn.coreboot.org/coreboot/trunk@5238 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1

1 files changed, 147 insertions, 6 deletions

diff --git a/src/northbridge/intel/i440bx/raminit.c b/src/northbridge/intel/i440bx/raminit.c
index 43e2a45e99..e77a35ac2c 100644
--- a/src/northbridge/intel/i440bx/raminit.c
+++ b/src/northbridge/intel/i440bx/raminit.c
@@ -431,15 +431,156 @@ static void do_ram_command(u32 command)
 
 static void set_dram_buffer_strength(void)
 {
-	/* TODO: This needs to be set according to the DRAM tech
-	 * (x8, x16, or x32). Argh, Intel provides no docs on this!
-	 * Currently, it needs to be pulled from the output of
-	 * lspci -xxx Rx92
+	/* To give some breathing room for romcc,
+	 * mbsc0 doubles as drb 
+	 * mbsc1 doubles as drb1
+	 * mbfs0 doubles as i and reg
+	 */
+	uint8_t mbsc0,mbsc1,mbsc3,mbsc4,mbfs0,mbfs2,fsb;
+
+	/* Tally how many rows between rows 0-3 and rows 4-7 are populated. 
+	 * This determines how to program MBFS and MBSC.
+	 */
+	uint8_t dimm03 = 0;
+	uint8_t dimm47 = 0;
+
+	mbsc0 = 0;
+	for (mbfs0 = DRB0; mbfs0 <= DRB7; mbfs0++) {
+		mbsc1 = pci_read_config8(NB, mbfs0);
+		if (mbsc0 != mbsc1) {
+			if (mbfs0 <= DRB3) {
+				dimm03++;
+			} else {
+				dimm47++;
+			}
+			mbsc0 = mbsc1;
+		}
+	}
+
+	/* Algorithm bitmap for programming MBSC[39:0] and MBFS[23:0]
+	 *
+	 * 440BX datasheet says buffer frequency is independent from bus frequency
+	 * and mismatch both ways are possible. This is how it is programmed
+	 * in ASUS P2B-LS.
 	 *
-	 * Relevant registers: MBSC, MBFS, BUFFC.
+	 * There are four main conditions to check when programming DRAM buffer
+	 * frequency and strength:
+	 *
+	 * a: >2 rows populated across DIMM0,1
+	 * b: >2 rows populated across DIMM2,3
+	 * c: >4 rows populated across all DIMM slots
+	 * and either one of:
+	 * 1: NBXCFG[13] strapped as 100MHz, or
+	 * 6: NBXCFG[13] strapped as 66MHz
+	 *
+	 * CKE0/FENA ----------------------------------------------------------+
+	 * CKE1/GCKE -------------------[    MBFS    ]------------------------+|
+	 * DQMA/CASA[764320]# ----------[ 0 = 66MHz  ]-----------------------+||
+	 * DQMB1/CASB1# ----------------[ 1 = 100MHz ]----------------------+|||
+	 * DQMB5/CASB5# ---------------------------------------------------+||||
+	 * DQMA1/CASA1# --------------------------------------------------+|||||
+	 * DQMA5/CASA5# -------------------------------------------------+||||||
+	 * CSA0-5#,CSB0-5# ----------------------------------------++++++|||||||
+	 * CSA6#/CKE2# -------------------------------------------+|||||||||||||
+	 * CSB6#/CKE4# ------------------------------------------+||||||||||||||
+	 * CSA7#/CKE3# -----------------------------------------+|||||||||||||||
+	 * CSB7#/CKE5# ----------------------------------------+||||||||||||||||
+	 * MECC[7:0] #2/#1 (100MHz) -------------------------++|||||||||||||||||
+	 * MD[63:0] #2/#1 (100MHz) ------------------------++|||||||||||||||||||
+	 * MAB[12:11,9:0]#,MAB[13,10],WEB#,SRASB#,SCASB# -+|||||||||||||||||||||
+	 * MAA[13:0],WEA#,SRASA#,SCASA# -----------------+||||||||||||||||||||||
+	 * Reserved ------------------------------------+|||||||||||||||||||||||
+	 *                                              ||||||||||||||||||||||||
+	 *   3        32        21        10        0 * 2  21        10        0
+	 *   9876543210987654321098765432109876543210 * 321098765432109876543210
+	 * a 10------------------------1010---------- * -1---------------11-----  a
+	 *!a 11------------------------1111---------- * -0---------------00----- !a
+	 * b --10--------------------------1010------ * --1----------------11---  b
+	 *!b --11--------------------------1111------ * --0----------------00--- !b
+	 * c ----------------------------------1100-- * ----------------------1-  c
+	 *!c ----------------------------------1011-- * ----------------------0- !c
+	 * 1 ----1010101000000000000000------------00 * ---11111111111111----1-0  1
+	 * 6 ----000000000000000000000010101010----00 * ---1111111111111100000-0  6
+	 *   | | | | | | | | | | ||||||| | | | | | |
+	 *   | | | | | | | | | | ||||||| | | | | | +- CKE0/FENA
+	 *   | | | | | | | | | | ||||||| | | | | +--- CKE1/GCKE
+	 *   | | | | | | | | | | ||||||| | | | +----- DQMA/CASA[764320]#
+	 *   | | | | | | | | | | ||||||| | | +------- DQMB1/CASB1#
+	 *   | | | | | | | | | | ||||||| | +--------- DQMB5/CASB5#
+	 *   | | | | | | | | | | ||||||| +----------- DQMA1/CASA1#
+	 *   | | | | | | | | | | ||||||+------------- DQMA5/CASA5#
+	 *   | | | | | | | | | | ++++++-------------- CSA0-5#,CSB0-5# [ 0=1x;1=2x ]
+	 *   | | | | | | | | | +--------------------- CSA6#/CKE2#
+	 *   | | | | | | | | +---[    MBSC    ]------ CSB6#/CKE4#
+	 *   | | | | | | | +-----[ 00 = 1x    ]------ CSA7#/CKE3#
+	 *   | | | | | | +-------[ 01 invalid ]------ CSB7#/CKE5#
+	 *   | | | | | +---------[ 10 = 2x    ]------ MECC[7:0] #1 (2x)
+	 *   | | | | +-----------[ 11 = 3x    ]------ MECC[7:0] #2 (2x)
+	 *   | | | +--------------------------------- MD[63:0] #1 (2x)
+	 *   | | +----------------------------------- MD[63:0] #2 (2x)
+	 *   | +------------------------------------- MAB[12:11,9:0]#,MAB[13,10],WEB#,SRASB#,SCASB#
+	 *   +--------------------------------------- MAA[13:0],WEA#,SRASA#,SCASA#
+	 * MBSC[47:40] and MBFS[23] are reserved.
+	 *
+	 * This algorithm is checked against P2B-LS factory BIOS. It has 4 DIMM slots.
+	 * Therefore it assumes a board with 4 slots, and will need testing
+	 * on boards with 3 DIMM slots.
 	 */
+	 
+	mbsc0 = 0x80;
+	mbsc1 = 0x2a;
+	mbfs2 = 0x1f;
+	if (pci_read_config8(NB, NBXCFG + 1) & 0x30) {
+		fsb = 66;
+		mbsc3 = 0x00;
+		mbsc4 = 0x00;
+		mbfs0 = 0x80;
+	} else {
+		fsb = 100;
+		mbsc3 = 0xa0;
+		mbsc4 = 0x0a;
+		mbfs0 = 0x84;
+	}
+	
+	if (dimm03 > 2) { 
+		mbsc4 = mbsc4 | 0x80; 
+		mbsc1 = mbsc1 | 0x28;
+		mbfs2 = mbfs2 | 0x40;
+		mbfs0 = mbfs0 | 0x60;
+	} else { 
+		mbsc4 = mbsc4 | 0xc0; 
+		if (fsb == 100) {
+			mbsc1 = mbsc1 | 0x3c;
+		}
+	}	
+	if (dimm47 > 2) { 
+		mbsc4 = mbsc4 | 0x20; 
+		mbsc1 = mbsc1 | 0x02; 
+		mbsc0 = mbsc0 | 0x80;
+		mbfs2 = mbfs2 | 0x20;
+		mbfs0 = mbfs0 | 0x18;
+	} else { 
+		mbsc4 = mbsc4 | 0x30;
+		if (fsb == 100) {
+			mbsc1 = mbsc1 | 0x03; 
+			mbsc0 = mbsc0 | 0xc0;
+		}
+	}
+	if ((dimm03 + dimm47) > 4) { 
+		mbsc0 = mbsc0 | 0x30;
+		mbfs0 = mbfs0 | 0x02;
+	} else { 
+		mbsc0 = mbsc0 | 0x2c; 
+	}
 
-	pci_write_config8(NB, MBSC, 0x03);
+	pci_write_config8(NB, MBSC + 0, mbsc0);
+	pci_write_config8(NB, MBSC + 1, mbsc1);
+	pci_write_config8(NB, MBSC + 2, 0x00);
+	pci_write_config8(NB, MBSC + 3, mbsc3);
+	pci_write_config8(NB, MBSC + 4, mbsc4);
+	pci_write_config8(NB, MBFS + 0, mbfs0);
+	pci_write_config8(NB, MBFS + 1, 0xff);
+	pci_write_config8(NB, MBFS + 2, mbfs2);
 }
 
 /*-----------------------------------------------------------------------------