sfc: PTP changes to support improved UUID filtering mode

There is a long-standing problem with the packet-timestamp matching in
the driver. When a PTP packet is received by the MC, the FPGA
timestamps the packet and the MC sends the timestamp and 6 bytes of
the UUID to the driver. The driver then matches the timestamp against
received packets using the same 6 bytes of UUID.

The problem comes from the choice of which 6 bytes to use. The PTP
spec is slightly contradictory and misleading in one of the two places
where the UUIDs are discussed. From section 7.2.2.2 of the spec, a
PTPD2 UUID can be either a EUI-64 or a EUI-64 constructed from a
EUI-48. The typical ethernet based implementation uses a EUI-64
constructed from a EUI-48. This works by taking the first 3 bytes of
the MAC address of the NIC being used for PTP (the OUI), then
inserting 0xFF, 0xFE, then taking the last 3 bytes of the MAC address
giving
          MAC[0], MAC[1], MAC[2], 0xFF, 0xFE, MAC[3], MAC[4], MAC[5]
The current MC firmware and driver discard the first two bytes of this
UUID and packets are matched against timestamps using bytes 2 to 7 so
there is a small risk that in a deployment of Solarflare PTP NICs used
with other vendors NICs, that a PTP packet could be matched against
the wrong timestamp. This applies to all other organisations whose
third byte of the OUI is 0x53. It's a long list but I notice that it
includes Cisco.

The necessary modifications to use bytes 0-2 and 5-7 of the UUID to
match against are quite small but introduce incompatibility between
older version of the firmware and driver.

When PTP is enabled via SO_TIMESTAMPING specifying PTP V2, the driver
will try to enable PTP in the firmware using the enhanced mode
(above). If the firmware returns an error, the driver will enable PTP
in the firmware using the old mode.

[bwh: Fix some style errors; remove private ioctl bits]
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/mcdi_pcol.h

@@ -553,6 +553,7 @@
 #define          MC_CMD_PTP_MODE_V1_VLAN 0x1 /* enum */
 #define          MC_CMD_PTP_MODE_V2 0x2 /* enum */
 #define          MC_CMD_PTP_MODE_V2_VLAN 0x3 /* enum */
+#define          MC_CMD_PTP_MODE_V2_ENHANCED 0x4 /* enum */
 
 /* MC_CMD_PTP_IN_DISABLE msgrequest */
 #define    MC_CMD_PTP_IN_DISABLE_LEN 8

drivers/net/ethernet/sfc/ptp.c

@@ -99,6 +99,9 @@
 #define PTP_V2_VERSION_LENGTH	1
 #define PTP_V2_VERSION_OFFSET	29
 
+#define PTP_V2_UUID_LENGTH	8
+#define PTP_V2_UUID_OFFSET	48
+
 /* Although PTP V2 UUIDs are comprised a ClockIdentity (8) and PortNumber (2),
  * the MC only captures the last six bytes of the clock identity. These values
  * reflect those, not the ones used in the standard.  The standard permits
@@ -1011,7 +1014,7 @@ static bool efx_ptp_rx(struct efx_channel *channel, struct sk_buff *skb)
 	struct efx_nic *efx = channel->efx;
 	struct efx_ptp_data *ptp = efx->ptp_data;
 	struct efx_ptp_match *match = (struct efx_ptp_match *)skb->cb;
-	u8 *data;
+	u8 *match_data_012, *match_data_345;
 	unsigned int version;
 
 	match->expiry = jiffies + msecs_to_jiffies(PKT_EVENT_LIFETIME_MS);
@@ -1025,21 +1028,35 @@ static bool efx_ptp_rx(struct efx_channel *channel, struct sk_buff *skb)
 		if (version != PTP_VERSION_V1) {
 			return false;
 		}
+
+		/* PTP V1 uses all six bytes of the UUID to match the packet
+		 * to the timestamp
+		 */
+		match_data_012 = skb->data + PTP_V1_UUID_OFFSET;
+		match_data_345 = skb->data + PTP_V1_UUID_OFFSET + 3;
 	} else {
 		if (skb->len < PTP_V2_MIN_LENGTH) {
 			return false;
 		}
 		version = skb->data[PTP_V2_VERSION_OFFSET];
-
-		BUG_ON(ptp->mode != MC_CMD_PTP_MODE_V2);
-		BUILD_BUG_ON(PTP_V1_UUID_OFFSET != PTP_V2_MC_UUID_OFFSET);
-		BUILD_BUG_ON(PTP_V1_UUID_LENGTH != PTP_V2_MC_UUID_LENGTH);
-		BUILD_BUG_ON(PTP_V1_SEQUENCE_OFFSET != PTP_V2_SEQUENCE_OFFSET);
-		BUILD_BUG_ON(PTP_V1_SEQUENCE_LENGTH != PTP_V2_SEQUENCE_LENGTH);
-
 		if ((version & PTP_VERSION_V2_MASK) != PTP_VERSION_V2) {
 			return false;
 		}
+
+		/* The original V2 implementation uses bytes 2-7 of
+		 * the UUID to match the packet to the timestamp. This
+		 * discards two of the bytes of the MAC address used
+		 * to create the UUID (SF bug 33070).  The PTP V2
+		 * enhanced mode fixes this issue and uses bytes 0-2
+		 * and byte 5-7 of the UUID.
+		 */
+		match_data_345 = skb->data + PTP_V2_UUID_OFFSET + 5;
+		if (ptp->mode == MC_CMD_PTP_MODE_V2) {
+			match_data_012 = skb->data + PTP_V2_UUID_OFFSET + 2;
+		} else {
+			match_data_012 = skb->data + PTP_V2_UUID_OFFSET + 0;
+			BUG_ON(ptp->mode != MC_CMD_PTP_MODE_V2_ENHANCED);
+		}
 	}
 
 	/* Does this packet require timestamping? */
@@ -1052,14 +1069,19 @@ static bool efx_ptp_rx(struct efx_channel *channel, struct sk_buff *skb)
 		timestamps = skb_hwtstamps(skb);
 		memset(timestamps, 0, sizeof(*timestamps));
 
+		/* We expect the sequence number to be in the same position in
+		 * the packet for PTP V1 and V2
+		 */
+		BUILD_BUG_ON(PTP_V1_SEQUENCE_OFFSET != PTP_V2_SEQUENCE_OFFSET);
+		BUILD_BUG_ON(PTP_V1_SEQUENCE_LENGTH != PTP_V2_SEQUENCE_LENGTH);
+
 		/* Extract UUID/Sequence information */
-		data = skb->data + PTP_V1_UUID_OFFSET;
-		match->words[0] = (data[0]         |
-				   (data[1] << 8)  |
-				   (data[2] << 16) |
-				   (data[3] << 24));
-		match->words[1] = (data[4]         |
-				   (data[5] << 8)  |
+		match->words[0] = (match_data_012[0]         |
+				   (match_data_012[1] << 8)  |
+				   (match_data_012[2] << 16) |
+				   (match_data_345[0] << 24));
+		match->words[1] = (match_data_345[1]         |
+				   (match_data_345[2] << 8)  |
 				   (skb->data[PTP_V1_SEQUENCE_OFFSET +
 					      PTP_V1_SEQUENCE_LENGTH - 1] <<
 				    16));
@@ -1165,7 +1187,7 @@ static int efx_ptp_ts_init(struct efx_nic *efx, struct hwtstamp_config *init)
 	 * timestamped
 	 */
 		init->rx_filter = HWTSTAMP_FILTER_PTP_V2_L4_EVENT;
-		new_mode = MC_CMD_PTP_MODE_V2;
+		new_mode = MC_CMD_PTP_MODE_V2_ENHANCED;
 		enable_wanted = true;
 		break;
 	case HWTSTAMP_FILTER_PTP_V2_EVENT:
@@ -1184,7 +1206,14 @@ static int efx_ptp_ts_init(struct efx_nic *efx, struct hwtstamp_config *init)
 	if (init->tx_type != HWTSTAMP_TX_OFF)
 		enable_wanted = true;
 
+	/* Old versions of the firmware do not support the improved
+	 * UUID filtering option (SF bug 33070).  If the firmware does
+	 * not accept the enhanced mode, fall back to the standard PTP
+	 * v2 UUID filtering.
+	 */
 	rc = efx_ptp_change_mode(efx, enable_wanted, new_mode);
+	if ((rc != 0) && (new_mode == MC_CMD_PTP_MODE_V2_ENHANCED))
+		rc = efx_ptp_change_mode(efx, enable_wanted, MC_CMD_PTP_MODE_V2);
 	if (rc != 0)
 		return rc;