net: stmmac: add aux timestamps fifo clearance wait

commit ae9dcb9 upstream.

Add timeout polling wait for auxiliary timestamps snapshot FIFO clear bit
(ATSFC) to clear. This is to ensure no residue fifo value is being read
erroneously.

Fixes: f4da565 ("net: stmmac: Add support for external trigger timestamping")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Noor Azura Ahmad Tarmizi <noor.azura.ahmad.tarmizi@intel.com>
Link: https://lore.kernel.org/r/20230111050200.2130-1-noor.azura.ahmad.tarmizi@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c

@@ -229,7 +229,10 @@ static int stmmac_enable(struct ptp_clock_info *ptp,
 		}
 		writel(acr_value, ptpaddr + PTP_ACR);
 		mutex_unlock(&priv->aux_ts_lock);
-		ret = 0;
+		/* wait for auxts fifo clear to finish */
+		ret = readl_poll_timeout(ptpaddr + PTP_ACR, acr_value,
+					 !(acr_value & PTP_ACR_ATSFC),
+					 10, 10000);
 		break;
 
 	default: