1 files changed, 43 insertions, 1 deletions

diff --git a/drivers/infiniband/hw/hfi1/platform.c b/drivers/infiniband/hw/hfi1/platform.c
index 0e7043801bb1..838fe84e285a 100644
--- a/drivers/infiniband/hw/hfi1/platform.c
+++ b/drivers/infiniband/hw/hfi1/platform.c
@@ -637,6 +637,38 @@ static void apply_tx_lanes(struct hfi1_pportdata *ppd, u8 field_id,
         }
 }
 
+/*
+ * Return a special SerDes setting for low power AOC cables.  The power class
+ * threshold and setting being used were all found by empirical testing.
+ *
+ * Summary of the logic:
+ *
+ * if (QSFP and QSFP_TYPE == AOC and QSFP_POWER_CLASS < 4)
+ *     return 0xe
+ * return 0; // leave at default
+ */
+static u8 aoc_low_power_setting(struct hfi1_pportdata *ppd)
+{
+        u8 *cache = ppd->qsfp_info.cache;
+        int power_class;
+
+        /* QSFP only */
+        if (ppd->port_type != PORT_TYPE_QSFP)
+                return 0; /* leave at default */
+
+        /* active optical cables only */
+        switch ((cache[QSFP_MOD_TECH_OFFS] & 0xF0) >> 4) {
+        case 0x0 ... 0x9: /* fallthrough */
+        case 0xC: /* fallthrough */
+        case 0xE:
+                /* active AOC */
+                power_class = get_qsfp_power_class(cache[QSFP_MOD_PWR_OFFS]);
+                if (power_class < QSFP_POWER_CLASS_4)
+                        return 0xe;
+        }
+        return 0; /* leave at default */
+}
+
 static void apply_tunings(
                 struct hfi1_pportdata *ppd, u32 tx_preset_index,
                 u8 tuning_method, u32 total_atten, u8 limiting_active)
@@ -705,7 +737,17 @@ static void apply_tunings(
                 tx_preset_index, TX_PRESET_TABLE_POSTCUR, &tx_preset, 4);
         postcur = tx_preset;
 
-        config_data = precur | (attn << 8) | (postcur << 16);
+        /*
+         * NOTES:
+         * o The aoc_low_power_setting is applied to all lanes even
+         *   though only lane 0's value is examined by the firmware.
+         * o A lingering low power setting after a cable swap does
+         *   not occur.  On cable unplug the 8051 is reset and
+         *   restarted on cable insert.  This resets all settings to
+         *   their default, erasing any previous low power setting.
+         */
+        config_data = precur | (attn << 8) | (postcur << 16) |
+                        (aoc_low_power_setting(ppd) << 24);
 
         apply_tx_lanes(ppd, TX_EQ_SETTINGS, config_data,
                        "Applying TX settings");