igc: Correct the launchtime offset

The launchtime offset should be corrected according to sections 7.5.2.6
Transmit Scheduling Latency of the Intel Ethernet I225/I226 Software
User Manual.

Software can compensate the latency between the transmission scheduling
and the time that packet is transmitted to the network by setting this
GTxOffset register. Without setting this register, there may be a
significant delay between the packet scheduling and the network point.

This patch helps to reduce the latency for each of the link speed.

Before:

10Mbps   : 11000 - 13800 nanosecond
100Mbps  : 1300 - 1700 nanosecond
1000Mbps : 190 - 600 nanosecond
2500Mbps : 1400 - 1700 nanosecond

After:

10Mbps   : less than 750 nanosecond
100Mbps  : less than 192 nanosecond
1000Mbps : less than 128 nanosecond
2500Mbps : less than 128 nanosecond

Test Setup:

Talker : Use l2_tai.c to generate the launchtime into packet payload.
Listener: Use timedump.c to compute the delta between packet arrival and
LaunchTime packet payload.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Acked-by: Sasha Neftin <sasha.neftin@intel.com>
Acked-by: Paul Menzel <pmenzel@molgen.mpg.de>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/drivers/net/ethernet/intel/igc/igc_tsn.c b/drivers/net/ethernet/intel/igc/igc_tsn.c
index 0fce22de2ab8..f975ed807da1 100644
--- a/drivers/net/ethernet/intel/igc/igc_tsn.c
+++ b/drivers/net/ethernet/intel/igc/igc_tsn.c
@@ -48,6 +48,35 @@ static unsigned int igc_tsn_new_flags(struct igc_adapter *adapter)
 	return new_flags;
 }
 
+void igc_tsn_adjust_txtime_offset(struct igc_adapter *adapter)
+{
+	struct igc_hw *hw = &adapter->hw;
+	u16 txoffset;
+
+	if (!is_any_launchtime(adapter))
+		return;
+
+	switch (adapter->link_speed) {
+	case SPEED_10:
+		txoffset = IGC_TXOFFSET_SPEED_10;
+		break;
+	case SPEED_100:
+		txoffset = IGC_TXOFFSET_SPEED_100;
+		break;
+	case SPEED_1000:
+		txoffset = IGC_TXOFFSET_SPEED_1000;
+		break;
+	case SPEED_2500:
+		txoffset = IGC_TXOFFSET_SPEED_2500;
+		break;
+	default:
+		txoffset = 0;
+		break;
+	}
+
+	wr32(IGC_GTXOFFSET, txoffset);
+}
+
 /* Returns the TSN specific registers to their default values after
  * the adapter is reset.
  */
@@ -57,6 +86,7 @@ static int igc_tsn_disable_offload(struct igc_adapter *adapter)
 	u32 tqavctrl;
 	int i;
 
+	wr32(IGC_GTXOFFSET, 0);
 	wr32(IGC_TXPBS, I225_TXPBSIZE_DEFAULT);
 	wr32(IGC_DTXMXPKTSZ, IGC_DTXMXPKTSZ_DEFAULT);