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>

drivers/net/ethernet/intel/igc/igc_defines.h

@@ -400,6 +400,15 @@
 #define IGC_DTXMXPKTSZ_TSN	0x19 /* 1600 bytes of max TX DMA packet size */
 #define IGC_DTXMXPKTSZ_DEFAULT	0x98 /* 9728-byte Jumbo frames */
 
+/* Transmit Scheduling Latency */
+/* Latency between transmission scheduling (LaunchTime) and the time
+ * the packet is transmitted to the network in nanosecond.
+ */
+#define IGC_TXOFFSET_SPEED_10	0x000034BC
+#define IGC_TXOFFSET_SPEED_100	0x00000578
+#define IGC_TXOFFSET_SPEED_1000	0x0000012C
+#define IGC_TXOFFSET_SPEED_2500	0x00000578
+
 /* Time Sync Interrupt Causes */
 #define IGC_TSICR_SYS_WRAP	BIT(0) /* SYSTIM Wrap around. */
 #define IGC_TSICR_TXTS		BIT(1) /* Transmit Timestamp. */

drivers/net/ethernet/intel/igc/igc_main.c

@@ -5381,6 +5381,13 @@ static void igc_watchdog_task(struct work_struct *work)
 				break;
 			}
 
+			/* Once the launch time has been set on the wire, there
+			 * is a delay before the link speed can be determined
+			 * based on link-up activity. Write into the register
+			 * as soon as we know the correct link speed.
+			 */
+			igc_tsn_adjust_txtime_offset(adapter);
+
 			if (adapter->link_speed != SPEED_1000)
 				goto no_wait;
 

drivers/net/ethernet/intel/igc/igc_regs.h

@@ -224,6 +224,7 @@
 /* Transmit Scheduling Registers */
 #define IGC_TQAVCTRL		0x3570
 #define IGC_TXQCTL(_n)		(0x3344 + 0x4 * (_n))
+#define IGC_GTXOFFSET		0x3310
 #define IGC_BASET_L		0x3314
 #define IGC_BASET_H		0x3318
 #define IGC_QBVCYCLET		0x331C

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);
 

drivers/net/ethernet/intel/igc/igc_tsn.h

@@ -6,5 +6,6 @@
 
 int igc_tsn_offload_apply(struct igc_adapter *adapter);
 int igc_tsn_reset(struct igc_adapter *adapter);
+void igc_tsn_adjust_txtime_offset(struct igc_adapter *adapter);
 
 #endif /* _IGC_BASE_H */