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authorAngel Pons <th3fanbus@gmail.com>2020-12-07 02:00:41 +0100
committerFelix Held <felix-coreboot@felixheld.de>2020-12-23 16:04:22 +0000
commit3aed6ac613c0625d81ac0d1d2d8ccc72952fbc06 (patch)
tree47632cd6c047f54e5a1e5e216c44c7f20a084db2 /src/northbridge/intel
parentc8ac2ccf80428b5dbfecfc2006849413ba4c3e87 (diff)
downloadcoreboot-3aed6ac613c0625d81ac0d1d2d8ccc72952fbc06.tar.xz
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>
Diffstat (limited to 'src/northbridge/intel')
-rw-r--r--src/northbridge/intel/sandybridge/raminit_common.c21
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);