iwlwifi: add a W/A for a scheduler hardware bug

In case we need to move the scheduler write pointer by
steps of 0x40, 0x80 or 0xc0, the scheduler gets stuck.
This leads to hardware error interrupts with status:
0x5A5A5A5A or alike.

In order to work around this, detect in the transport
layer that we are going to hit this case and tell iwlmvm
to increment the sequence number of the packets. This
allows to keep the requirement that the WiFi sequence
number is in sync with the index in the scheduler Tx queue
and it also allows to avoid the problematic sequence.
This means that from time to time, we will start a queue
from ssn + 1, but that shouldn't be a problem since we
don't switch to new queues for AMPDU now that we have
DQA which allows to keep the same queue while toggling
the AMPDU state.

This bug has been fixed on 9000 devices and up.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/sta.c b/drivers/net/wireless/intel/iwlwifi/mvm/sta.c
index 0249300c4600..aa41ee8ed916 100644
--- a/drivers/net/wireless/intel/iwlwifi/mvm/sta.c
+++ b/drivers/net/wireless/intel/iwlwifi/mvm/sta.c
@@ -758,7 +758,7 @@ static int iwl_mvm_sta_alloc_queue(struct iwl_mvm *mvm,
 	bool using_inactive_queue = false, same_sta = false;
 	unsigned long disable_agg_tids = 0;
 	enum iwl_mvm_agg_state queue_state;
-	bool shared_queue = false;
+	bool shared_queue = false, inc_ssn;
 	int ssn;
 	unsigned long tfd_queue_mask;
 	int ret;
@@ -885,8 +885,12 @@ static int iwl_mvm_sta_alloc_queue(struct iwl_mvm *mvm,
 	}
 
 	ssn = IEEE80211_SEQ_TO_SN(le16_to_cpu(hdr->seq_ctrl));
-	iwl_mvm_enable_txq(mvm, queue, mac_queue, ssn, &cfg,
-			   wdg_timeout);
+	inc_ssn = iwl_mvm_enable_txq(mvm, queue, mac_queue,
+				     ssn, &cfg, wdg_timeout);
+	if (inc_ssn) {
+		ssn = (ssn + 1) & IEEE80211_SCTL_SEQ;
+		le16_add_cpu(&hdr->seq_ctrl, 0x10);
+	}
 
 	/*
 	 * Mark queue as shared in transport if shared
@@ -898,6 +902,13 @@ static int iwl_mvm_sta_alloc_queue(struct iwl_mvm *mvm,
 		iwl_trans_txq_set_shared_mode(mvm->trans, queue, true);
 
 	spin_lock_bh(&mvmsta->lock);
+	/*
+	 * This looks racy, but it is not. We have only one packet for
+	 * this ra/tid in our Tx path since we stop the Qdisc when we
+	 * need to allocate a new TFD queue.
+	 */
+	if (inc_ssn)
+		mvmsta->tid_data[tid].seq_number += 0x10;
 	mvmsta->tid_data[tid].txq_id = queue;
 	mvmsta->tid_data[tid].is_tid_active = true;
 	mvmsta->tfd_queue_msk |= BIT(queue);