net: macb: Optimize reading HW timestamp

The seconds input from BD (6 bits) just needs to be ORed with the
upper bits from timer in this function. Avoid addition operation
every single time. Seconds rollover handling is left untouched.
Signed-off-by: Harini Katakam <harini.katakam@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/cadence/macb_ptp.c

@@ -258,6 +258,8 @@ static int gem_hw_timestamp(struct macb *bp, u32 dma_desc_ts_1,
 	 */
 	gem_tsu_get_time(&bp->ptp_clock_info, &tsu, NULL);
 
+	ts->tv_sec |= ((~GEM_DMA_SEC_MASK) & tsu.tv_sec);
+
 	/* If the top bit is set in the timestamp,
 	 * but not in 1588 timer, it has rolled over,
 	 * so subtract max size
@@ -266,8 +268,6 @@ static int gem_hw_timestamp(struct macb *bp, u32 dma_desc_ts_1,
 	    !(tsu.tv_sec & (GEM_DMA_SEC_TOP >> 1)))
 		ts->tv_sec -= GEM_DMA_SEC_TOP;
 
-	ts->tv_sec += ((~GEM_DMA_SEC_MASK) & tsu.tv_sec);
-
 	return 0;
 }