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nb/intel/sandybridge/raminit: Fix CAS Write Latency

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As documented in DDR3 spec for MR2 the CWL is based on DDR frequency.
There's no to little difference for most memory modules operating at DDR3-1333.

It might fix problems for memory modules that operate at a higher frequency and
memory modules with low CL values should work even better.

Tested on Lenovo T420 with DDR3-1333 CL9 and DDR3-1600 CL11.
No regressions found.

Change-Id: Ib90b5de872a219cf80b4976b6dfae6bc02e298f4
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/17389
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
This commit is contained in:
Patrick Rudolph 2016-11-11 19:17:56 +01:00
parent 78c5f0cc02
commit bec669685c
1 changed files with 27 additions and 11 deletions
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38
src/northbridge/intel/sandybridge/raminit.c
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@ -491,17 +491,33 @@ static void dram_find_common_params(ramctr_timing *ctrl)
die("No valid DIMMs found"); die("No valid DIMMs found");
} }
static u8 get_CWL(u8 CAS) /* CAS write latency. To be programmed in MR2.
* See DDR3 SPEC for MR2 documentation. */
static u8 get_CWL(u32 tCK)
{ {
/* Get CWL based on CAS using the following rule: /* Get CWL based on tCK using the following rule: */
* _________________________________________ switch (tCK) {
* CAS: | 4T | 5T | 6T | 7T | 8T | 9T | 10T | 11T | case TCK_1333MHZ:
* CWL: | 5T | 5T | 5T | 6T | 6T | 7T | 7T | 8T | return 12;
*/ case TCK_1200MHZ:
static const u8 cas_cwl_map[] = { 5, 5, 5, 6, 6, 7, 7, 8 }; case TCK_1100MHZ:
if (CAS > 11) return 11;
case TCK_1066MHZ:
case TCK_1000MHZ:
return 10;
case TCK_933MHZ:
case TCK_900MHZ:
return 9;
case TCK_800MHZ:
case TCK_700MHZ:
return 8; return 8;
return cas_cwl_map[CAS - 4]; case TCK_666MHZ:
return 7;
case TCK_533MHZ:
return 6;
default:
return 5;
}
} }
/* Frequency multiplier. */ /* Frequency multiplier. */
@ -713,7 +729,7 @@ static void dram_timing(ramctr_timing * ctrl)
val32 = (1000 << 8) / ctrl->tCK; val32 = (1000 << 8) / ctrl->tCK;
printk(BIOS_DEBUG, "Selected DRAM frequency: %u MHz\n", val32); printk(BIOS_DEBUG, "Selected DRAM frequency: %u MHz\n", val32);
/* Find CAS and CWL latencies */ /* Find CAS latency */
val = (ctrl->tAA + ctrl->tCK - 1) / ctrl->tCK; val = (ctrl->tAA + ctrl->tCK - 1) / ctrl->tCK;
printk(BIOS_DEBUG, "Minimum CAS latency : %uT\n", val); printk(BIOS_DEBUG, "Minimum CAS latency : %uT\n", val);
/* Find lowest supported CAS latency that satisfies the minimum value */ /* Find lowest supported CAS latency that satisfies the minimum value */
@ -734,7 +750,7 @@ static void dram_timing(ramctr_timing * ctrl)
printk(BIOS_DEBUG, "Selected CAS latency : %uT\n", val); printk(BIOS_DEBUG, "Selected CAS latency : %uT\n", val);
ctrl->CAS = val; ctrl->CAS = val;
ctrl->CWL = get_CWL(ctrl->CAS); ctrl->CWL = get_CWL(ctrl->tCK);
printk(BIOS_DEBUG, "Selected CWL latency : %uT\n", ctrl->CWL); printk(BIOS_DEBUG, "Selected CWL latency : %uT\n", ctrl->CWL);
/* Find tRCD */ /* Find tRCD */