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| author | Angel Pons <th3fanbus@gmail.com> | 2020-12-07 02:00:41 +0100 |
|---|---|---|
| committer | Felix Held <felix-coreboot@felixheld.de> | 2020-12-23 16:04:22 +0000 |
| commit | 3aed6ac613c0625d81ac0d1d2d8ccc72952fbc06 (patch) | |
| tree | 47632cd6c047f54e5a1e5e216c44c7f20a084db2 | |
| parent | c8ac2ccf80428b5dbfecfc2006849413ba4c3e87 (diff) | |
nb/intel/sandybridge: Add comments about I/O and RT latency
Document the algorithm to adjust I/O and roundtrip latencies.
Change-Id: Ic8b9aed54a34bb3252c457e87e81387fd410e305
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48397
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
| -rw-r--r-- | src/northbridge/intel/sandybridge/raminit_common.c | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/src/northbridge/intel/sandybridge/raminit_common.c b/src/northbridge/intel/sandybridge/raminit_common.c index d24e5a8883..70a856c7d1 100644 --- a/src/northbridge/intel/sandybridge/raminit_common.c +++ b/src/northbridge/intel/sandybridge/raminit_common.c @@ -1059,6 +1059,7 @@ static void test_rcven(ramctr_timing *ctrl, int channel, int slotrank) { wait_for_iosav(channel); + /* Send a burst of 16 back-to-back read commands (4 DCLK apart) */ iosav_write_read_mpr_sequence(channel, slotrank, ctrl->tMOD, 1, 3, 15, ctrl->CAS + 36); /* Execute command queue */ @@ -1193,6 +1194,12 @@ static void fine_tune_rcven_pi(ramctr_timing *ctrl, int channel, int slotrank, i } } +/* + * Once the DQS high phase has been found (for each DRAM) the next stage + * is to find out the round trip latency, by locating the preamble cycle. + * This is achieved by trying smaller and smaller roundtrip values until + * the strobe sampling is done on the preamble cycle. + */ static int find_roundtrip_latency(ramctr_timing *ctrl, int channel, int slotrank, int *upperA) { int works[NUM_LANES]; @@ -1212,10 +1219,17 @@ static int find_roundtrip_latency(ramctr_timing *ctrl, int channel, int slotrank else all_works = 0; } + + /* If every lane is working, exit */ if (all_works) return 0; + /* + * If all bits are one (everyone is failing), decrement + * the roundtrip value by two, and do another iteration. + */ if (!some_works) { + /* Guard against roundtrip latency underflow */ if (ctrl->timings[channel][slotrank].roundtrip_latency < 2) { printk(BIOS_EMERG, "402x discovery failed (1): %d, %d\n", channel, slotrank); @@ -1225,9 +1239,16 @@ static int find_roundtrip_latency(ramctr_timing *ctrl, int channel, int slotrank printram("4024 -= 2;\n"); continue; } + + /* + * Else (if some lanes are failing), increase the rank's + * I/O latency by 2, and increase rcven logic delay by 2 + * on the working lanes, then perform another iteration. + */ ctrl->timings[channel][slotrank].io_latency += 2; printram("4028 += 2;\n"); + /* Guard against I/O latency overflow */ if (ctrl->timings[channel][slotrank].io_latency >= 0x10) { printk(BIOS_EMERG, "402x discovery failed (2): %d, %d\n", channel, slotrank); |