igb: Fix the transmission mode of queue 0 for Qav mode

When Qav mode is enabled, queue 0 should be kept on Stream Reservation
mode. From the i210 datasheet, section 8.12.19:

"Note: Queue0 QueueMode must be set to 1b when TransmitMode is set to
Qav." ("QueueMode 1b" represents the Stream Reservation mode)

The solution is to give queue 0 the all the credits it might need, so
it has priority over queue 1.

A situation where this can happen is when cbs is "installed" only on
queue 1, leaving queue 0 alone. For example:

$ tc qdisc replace dev enp2s0 handle 100: parent root mqprio num_tc 3 \
     	   map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 queues 1@0 1@1 2@2 hw 0

$ tc qdisc replace dev enp2s0 parent 100:2 cbs locredit -1470 \
     	   hicredit 30 sendslope -980000 idleslope 20000 offload 1

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index c1c0bc30a16d8196f8319a21dcb1f8d13ef4ac52..cce7ada8925510b81d7f3e996a1b9e63d32bcd86 100644 (file)
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -1700,7 +1700,22 @@ static void igb_configure_cbs(struct igb_adapter *adapter, int queue,
        WARN_ON(hw->mac.type != e1000_i210);
        WARN_ON(queue < 0 || queue > 1);
 
-       if (enable) {
+       if (enable || queue == 0) {
+               /* i210 does not allow the queue 0 to be in the Strict
+                * Priority mode while the Qav mode is enabled, so,
+                * instead of disabling strict priority mode, we give
+                * queue 0 the maximum of credits possible.
+                *
+                * See section 8.12.19 of the i210 datasheet, "Note:
+                * Queue0 QueueMode must be set to 1b when
+                * TransmitMode is set to Qav."
+                */
+               if (queue == 0 && !enable) {
+                       /* max "linkspeed" idleslope in kbps */
+                       idleslope = 1000000;
+                       hicredit = ETH_FRAME_LEN;
+               }
+
                set_tx_desc_fetch_prio(hw, queue, TX_QUEUE_PRIO_HIGH);
                set_queue_mode(hw, queue, QUEUE_MODE_STREAM_RESERVATION);