cxgb4: fix large delays in PTP synchronization

Fetching PTP sync information from mailbox is slow and can take
up to 10 milliseconds. Reduce this unnecessary delay by directly
reading the information from the corresponding registers.

Fixes: 9c33e420 ("cxgb4: Add PTP Hardware Clock (PHC) support")
Signed-off-by: Manoj Malviya <manojmalviya@chelsio.com>
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_ptp.c

@@ -311,32 +311,17 @@ static int cxgb4_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
  */
 static int cxgb4_ptp_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
 {
-	struct adapter *adapter = (struct adapter *)container_of(ptp,
-				   struct adapter, ptp_clock_info);
-	struct fw_ptp_cmd c;
+	struct adapter *adapter = container_of(ptp, struct adapter,
+					       ptp_clock_info);
 	u64 ns;
-	int err;
-
-	memset(&c, 0, sizeof(c));
-	c.op_to_portid = cpu_to_be32(FW_CMD_OP_V(FW_PTP_CMD) |
-				     FW_CMD_REQUEST_F |
-				     FW_CMD_READ_F |
-				     FW_PTP_CMD_PORTID_V(0));
-	c.retval_len16 = cpu_to_be32(FW_CMD_LEN16_V(sizeof(c) / 16));
-	c.u.ts.sc = FW_PTP_SC_GET_TIME;
 
-	err = t4_wr_mbox(adapter, adapter->mbox, &c, sizeof(c), &c);
-	if (err < 0) {
-		dev_err(adapter->pdev_dev,
-			"PTP: %s error %d\n", __func__, -err);
-		return err;
-	}
+	ns = t4_read_reg(adapter, T5_PORT_REG(0, MAC_PORT_PTP_SUM_LO_A));
+	ns |= (u64)t4_read_reg(adapter,
+			       T5_PORT_REG(0, MAC_PORT_PTP_SUM_HI_A)) << 32;
 
 	/* convert to timespec*/
-	ns = be64_to_cpu(c.u.ts.tm);
 	*ts = ns_to_timespec64(ns);
-
-	return err;
+	return 0;
 }
 
 /**

drivers/net/ethernet/chelsio/cxgb4/t4_regs.h

@@ -1906,6 +1906,9 @@
 
 #define MAC_PORT_CFG2_A 0x818
 
+#define MAC_PORT_PTP_SUM_LO_A 0x990
+#define MAC_PORT_PTP_SUM_HI_A 0x994
+
 #define MPS_CMN_CTL_A	0x9000
 
 #define COUNTPAUSEMCRX_S    5