[RESEND PATCH 2/2] net: macb: Optimize reading HW timestamp

[Harini Katakam]

From: Harini Katakam <harini.katakam@xxxxxxxxxx>

The seconds input from BD (6 bits) just needs to be ORed with the
upper bits from timer in this function. Avoid +/- operations every
single time. Check for seconds rollover at BIT 5 and subtract the
overhead only in that case.

Signed-off-by: Harini Katakam <harini.katakam@xxxxxxxxxx>
Signed-off-by: Michal Simek <michal.simek@xxxxxxxxxx>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxxxxx>
Acked-by: Richard Cochran <richardcochran@xxxxxxxxx>
---
 drivers/net/ethernet/cadence/macb_ptp.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_ptp.c b/drivers/net/ethernet/cadence/macb_ptp.c
index e6cb20aaa76a..674002661366 100644
--- a/drivers/net/ethernet/cadence/macb_ptp.c
+++ b/drivers/net/ethernet/cadence/macb_ptp.c
@@ -247,6 +247,7 @@ static int gem_hw_timestamp(struct macb *bp, u32 dma_desc_ts_1,
 			    u32 dma_desc_ts_2, struct timespec64 *ts)
 {
 	struct timespec64 tsu;
+	bool sec_rollover = false;
 
 	ts->tv_sec = (GEM_BFEXT(DMA_SECH, dma_desc_ts_2) << GEM_DMA_SECL_SIZE) |
 			GEM_BFEXT(DMA_SECL, dma_desc_ts_1);
@@ -264,9 +265,12 @@ static int gem_hw_timestamp(struct macb *bp, u32 dma_desc_ts_1,
 	 */
 	if ((ts->tv_sec & (GEM_DMA_SEC_TOP >> 1)) &&
 	    !(tsu.tv_sec & (GEM_DMA_SEC_TOP >> 1)))
-		ts->tv_sec -= GEM_DMA_SEC_TOP;
+		sec_rollover = true;
+
+	ts->tv_sec |= ((~GEM_DMA_SEC_MASK) & tsu.tv_sec);
 
-	ts->tv_sec += ((~GEM_DMA_SEC_MASK) & tsu.tv_sec);
+	if (sec_rollover)
+		ts->tv_sec -= GEM_DMA_SEC_TOP;
 
 	return 0;
 }
-- 
2.17.1