[coreboot-gerrit] New patch to review for coreboot: [WIP] device/dram/ddr3: add FTB timings

[Nicola Corna (nicola@corna.info)]

Nicola Corna (nicola at corna.info) just uploaded a new patch set to gerrit, which you can find at https://review.coreboot.org/17476

-gerrit

commit c2a7f715a961873f378bcdd47a5ace8b4aa2e198
Author: Nicola Corna <nicola at corna.info>
Date:   Wed Nov 16 08:57:15 2016 +0100

    [WIP] device/dram/ddr3: add FTB timings
    
    SPD revision 1.1 introduced FTB timings, an extra set of SPD values that
    specify a more precise tCKmin, tAAmin, tRCDmin, tRPmin and tRCmin.
    
    For backwards compatibility, the MTB is usually rounded up and the FTB
    part is negative. For this reason some memories were not set up optimally,
    as the FTB part was ignored and the resulting timing wasn't set to the
    minimum value.
    
    The tests were performed on a Lenovo X220 with two Micron 8KTF51264HZ-1G9E
    (1866 MHz): reading only the MTB part, Coreboot reported a tCKmin of
    1.125 ns, corresponding to a working frequency of 800 MHz; with the
    additional tCKmin FTB part (-0.054 ns) the new (rounded) value is
    1.070 ns, valid for a 933 MHz operation.
    
    Some manufacturers (like Micron) seems to expect a small rounding on the
    timings, so a nearest-value rounding is performed. If this assumption
    isn't correct, an error up to ~2 ps can be committed, which is low enough
    to be safely ignored.
    
    Change-Id: Ib98f2e70820f207429d04ca6421680109a81f457
    Signed-off-by: Nicola Corna <nicola at corna.info>
---
 src/device/dram/ddr3.c | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/src/device/dram/ddr3.c b/src/device/dram/ddr3.c
index cb5b685..57e25d8 100644
--- a/src/device/dram/ddr3.c
+++ b/src/device/dram/ddr3.c
@@ -2,6 +2,7 @@
  * This file is part of the coreboot project.
  *
  * Copyright (C) 2011-2013  Alexandru Gagniuc <mr.nuke.me at gmail.com>
+ * Copyright (C) 2016 Nicola Corna <nicola at corna.info>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -108,9 +109,10 @@ int spd_decode_ddr3(dimm_attr * dimm, spd_raw_data spd)
 {
 	int ret;
 	u16 crc, spd_crc;
-	u8 ftb_divisor, ftb_dividend, capacity_shift, bus_width;
+	u8 capacity_shift, bus_width;
 	u8 reg8;
 	u32 mtb;		/* medium time base */
+	u32 ftb;		/* fine time base */
 	unsigned int val, param;
 
 	ret = SPD_STATUS_OK;
@@ -242,12 +244,6 @@ int spd_decode_ddr3(dimm_attr * dimm, spd_raw_data spd)
 	dimm->size_mb = ((1 << (capacity_shift + (25 - 20))) * bus_width
 			 * dimm->ranks) / dimm->width;
 
-	/* Fine Timebase (FTB) Dividend/Divisor */
-	/* Dividend */
-	ftb_dividend = (spd[9] >> 4) & 0x0f;
-	/* Divisor */
-	ftb_divisor = spd[9] & 0x0f;
-
 	/* Medium Timebase =
 	 *   Medium Timebase (MTB) Dividend /
 	 *   Medium Timebase (MTB) Divisor */
@@ -280,6 +276,29 @@ int spd_decode_ddr3(dimm_attr * dimm, spd_raw_data spd)
 	/* Minimum Four Activate Window Delay Time (tFAWmin) */
 	dimm->tFAW = (((spd[28] & 0x0f) << 8) + spd[29]) * mtb;
 
+	/* FTB is introduced in SPD revision 1.1 */
+	if (spd[1] >= 0x11 && spd[9])
+	{
+		/* Fine timebase (1/256 ps) =
+		 *   Fine Timebase (FTB) Dividend /
+		 *   Fine Timebase (FTB) Divisor */
+		ftb = (((u16) spd[9] & 0xf0) << 4) / (spd[9] & 0x0f);
+
+		/* SPD recommends to round up the MTB part and use a negative
+		 * FTB, so a negative rounding should be always safe */
+
+		/* SDRAM Minimum Cycle Time (tCKmin) correction */
+		dimm->tCK +=(s32)((s8) spd[34] * ftb - 500) / 1000;
+		/* Minimum CAS Latency Time (tAAmin) correction */
+		dimm->tAA += (s32)((s8) spd[35] * ftb - 500) / 1000;
+		/* Minimum RAS# to CAS# Delay Time (tRCDmin) correction */
+		dimm->tRCD += (s32)((s8) spd[36] * ftb - 500) / 1000;
+		/* Minimum Row Precharge Delay Time (tRPmin) correction */
+		dimm->tRP += (s32)((s8) spd[37] * ftb - 500) / 1000;
+		/* Minimum Active to Active/Refresh Delay Time (tRCmin) corr. */
+		dimm->tRC += (s32)((s8) spd[38] * ftb - 500) / 1000;
+	}
+
 	/* SDRAM Optional Features */
 	reg8 = spd[30];
 	printram("  Optional features  :");