igc: Add launch time support to XDP ZC

Enable Launch Time Control (LTC) support for XDP zero copy via XDP Tx
metadata framework.

This patch has been tested with tools/testing/selftests/bpf/xdp_hw_metadata
on Intel I225-LM Ethernet controller. Below are the test steps and result.

Test 1: Send a single packet with the launch time set to 1 s in the future.

Test steps:
1. On the DUT, start the xdp_hw_metadata selftest application:
   $ sudo ./xdp_hw_metadata enp2s0 -l 1000000000 -L 1

2. On the Link Partner, send a UDP packet with VLAN priority 1 to port 9091
   of the DUT.

Result:
When the launch time is set to 1 s in the future, the delta between the
launch time and the transmit hardware timestamp is 0.016 us, as shown in
printout of the xdp_hw_metadata application below.
  0x562ff5dc8880: rx_desc[4]->addr=84110 addr=84110 comp_addr=84110 EoP
  rx_hash: 0xE343384 with RSS type:0x1
  HW RX-time:   1734578015467548904 (sec:1734578015.4675)
                delta to User RX-time sec:0.0002 (183.103 usec)
  XDP RX-time:   1734578015467651698 (sec:1734578015.4677)
                 delta to User RX-time sec:0.0001 (80.309 usec)
  No rx_vlan_tci or rx_vlan_proto, err=-95
  0x562ff5dc8880: ping-pong with csum=561c (want c7dd)
                  csum_start=34 csum_offset=6
  HW RX-time:   1734578015467548904 (sec:1734578015.4675)
                delta to HW Launch-time sec:1.0000 (1000000.000 usec)
  0x562ff5dc8880: complete tx idx=4 addr=4018
  HW Launch-time:   1734578016467548904 (sec:1734578016.4675)
                    delta to HW TX-complete-time sec:0.0000 (0.016 usec)
  HW TX-complete-time:   1734578016467548920 (sec:1734578016.4675)
                         delta to User TX-complete-time sec:0.0000
                         (32.546 usec)
  XDP RX-time:   1734578015467651698 (sec:1734578015.4677)
                 delta to User TX-complete-time sec:0.9999
                 (999929.768 usec)
  HW RX-time:   1734578015467548904 (sec:1734578015.4675)
                delta to HW TX-complete-time sec:1.0000 (1000000.016 usec)
  0x562ff5dc8880: complete rx idx=132 addr=84110

Test 2: Send 1000 packets with a 10 ms interval and the launch time set to
        500 us in the future.

Test steps:
1. On the DUT, start the xdp_hw_metadata selftest application:
   $ sudo chrt -f 99 ./xdp_hw_metadata enp2s0 -l 500000 -L 1 > \
     /dev/shm/result.log

2. On the Link Partner, send 1000 UDP packets with a 10 ms interval and
   VLAN priority 1 to port 9091 of the DUT.

Result:
When the launch time is set to 500 us in the future, the average delta
between the launch time and the transmit hardware timestamp is 0.016 us,
as shown in the analysis of /dev/shm/result.log below. The XDP launch time
works correctly in sending 1000 packets continuously.
  Min delta: 0.005 us
  Avr delta: 0.016 us
  Max delta: 0.031 us
  Total packets forwarded: 1000

Signed-off-by: Song Yoong Siang <[email protected]>
Reviewed-by: Faizal Rahim <[email protected]>

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

@@ -2951,9 +2951,33 @@ static u64 igc_xsk_fill_timestamp(void *_priv)
 	return *(u64 *)_priv;
 }
 
+static void igc_xsk_request_launch_time(u64 launch_time, void *_priv)
+{
+	struct igc_metadata_request *meta_req = _priv;
+	struct igc_ring *tx_ring = meta_req->tx_ring;
+	__le32 launch_time_offset;
+	bool insert_empty = false;
+	bool first_flag = false;
+
+	if (!tx_ring->launchtime_enable)
+		return;
+
+	launch_time_offset = igc_tx_launchtime(tx_ring,
+					       ns_to_ktime(launch_time),
+					       &first_flag, &insert_empty);
+	if (insert_empty) {
+		igc_insert_empty_packet(tx_ring);
+		meta_req->tx_buffer =
+			&tx_ring->tx_buffer_info[tx_ring->next_to_use];
+	}
+
+	igc_tx_ctxtdesc(tx_ring, launch_time_offset, first_flag, 0, 0, 0);
+}
+
 const struct xsk_tx_metadata_ops igc_xsk_tx_metadata_ops = {
 	.tmo_request_timestamp		= igc_xsk_request_timestamp,
 	.tmo_fill_timestamp		= igc_xsk_fill_timestamp,
+	.tmo_request_launch_time	= igc_xsk_request_launch_time,
 };
 
 static void igc_xdp_xmit_zc(struct igc_ring *ring)
@@ -2976,7 +3000,13 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 	ntu = ring->next_to_use;
 	budget = igc_desc_unused(ring);
 
-	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget--) {
+	/* Packets with launch time require one data descriptor and one context
+	 * descriptor. When the launch time falls into the next Qbv cycle, we
+	 * may need to insert an empty packet, which requires two more
+	 * descriptors. Therefore, to be safe, we always ensure we have at least
+	 * 4 descriptors available.
+	 */
+	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >= 4) {
 		struct igc_metadata_request meta_req;
 		struct xsk_tx_metadata *meta = NULL;
 		struct igc_tx_buffer *bi;
@@ -3000,6 +3030,12 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 		xsk_tx_metadata_request(meta, &igc_xsk_tx_metadata_ops,
 					&meta_req);
 
+		/* xsk_tx_metadata_request() may have updated next_to_use */
+		ntu = ring->next_to_use;
+
+		/* xsk_tx_metadata_request() may have updated Tx buffer info */
+		bi = meta_req.tx_buffer;
+
 		tx_desc = IGC_TX_DESC(ring, ntu);
 		tx_desc->read.cmd_type_len = cpu_to_le32(meta_req.cmd_type);
 		tx_desc->read.olinfo_status = cpu_to_le32(olinfo_status);
@@ -3017,9 +3053,11 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 		ntu++;
 		if (ntu == ring->count)
 			ntu = 0;
+
+		ring->next_to_use = ntu;
+		budget = igc_desc_unused(ring);
 	}
 
-	ring->next_to_use = ntu;
 	if (tx_desc) {
 		igc_flush_tx_descriptors(ring);
 		xsk_tx_release(pool);