[PATCH net-next v2 1/2] bnxt_en: cache only 24 bits of hw counter

[Vadim Fedorenko <vadfed@meta.com>]

This hardware can provide only 48 bits of cycle counter. We can leave
only 24 bits in the cache to extend RX timestamps from 32 bits to 48
bits. This make cache writes atomic even on 32 bit platforms and we can
simply use READ_ONCE()/WRITE_ONCE() pair and remove spinlock. The
configuration structure will be also reduced by 4 bytes.

Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c |  8 ++++----
 drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h | 16 +---------------
 2 files changed, 5 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
index fa514be87650..c7e626b9098a 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.c
@@ -106,7 +106,7 @@ static void bnxt_ptp_get_current_time(struct bnxt *bp)
 	if (!ptp)
 		return;
 	spin_lock_irqsave(&ptp->ptp_lock, flags);
-	WRITE_ONCE(ptp->old_time, ptp->current_time);
+	WRITE_ONCE(ptp->old_time, (u32)(ptp->current_time >> 24));
 	bnxt_refclk_read(bp, NULL, &ptp->current_time);
 	spin_unlock_irqrestore(&ptp->ptp_lock, flags);
 }
@@ -174,7 +174,7 @@ void bnxt_ptp_update_current_time(struct bnxt *bp)
 	struct bnxt_ptp_cfg *ptp = bp->ptp_cfg;
 
 	bnxt_refclk_read(ptp->bp, NULL, &ptp->current_time);
-	WRITE_ONCE(ptp->old_time, ptp->current_time);
+	WRITE_ONCE(ptp->old_time, (u32)(ptp->current_time >> 24));
 }
 
 static int bnxt_ptp_adjphc(struct bnxt_ptp_cfg *ptp, s64 delta)
@@ -813,7 +813,7 @@ int bnxt_get_rx_ts_p5(struct bnxt *bp, u64 *ts, u32 pkt_ts)
 	if (!ptp)
 		return -ENODEV;
 
-	BNXT_READ_TIME64(ptp, time, ptp->old_time);
+	time = (u64)(READ_ONCE(ptp->old_time) << 24);
 	*ts = (time & BNXT_HI_TIMER_MASK) | pkt_ts;
 	if (pkt_ts < (time & BNXT_LO_TIMER_MASK))
 		*ts += BNXT_LO_TIMER_MASK + 1;
@@ -1079,7 +1079,7 @@ int bnxt_ptp_init(struct bnxt *bp, bool phc_cfg)
 
 		spin_lock_irqsave(&ptp->ptp_lock, flags);
 		bnxt_refclk_read(bp, NULL, &ptp->current_time);
-		WRITE_ONCE(ptp->old_time, ptp->current_time);
+		WRITE_ONCE(ptp->old_time, (u32)(ptp->current_time >> 24));
 		spin_unlock_irqrestore(&ptp->ptp_lock, flags);
 		ptp_schedule_worker(ptp->ptp_clock, 0);
 	}
diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h
index f322466ecad3..80046bd314db 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h
@@ -106,10 +106,10 @@ struct bnxt_ptp_cfg {
 	/* serialize ts tx request queuing */
 	spinlock_t		ptp_tx_lock;
 	u64			current_time;
-	u64			old_time;
 	unsigned long		next_period;
 	unsigned long		next_overflow_check;
 	u32			cmult;
+	u32			old_time;
 	/* a 23b shift cyclecounter will overflow in ~36 mins.  Check overflow every 18 mins. */
 	#define BNXT_PHC_OVERFLOW_PERIOD	(18 * 60 * HZ)
 
@@ -145,20 +145,6 @@ struct bnxt_ptp_cfg {
 	struct bnxt_ptp_stats	stats;
 };
 
-#if BITS_PER_LONG == 32
-#define BNXT_READ_TIME64(ptp, dst, src)				\
-do {								\
-	unsigned long flags;					\
-								\
-	spin_lock_irqsave(&(ptp)->ptp_lock, flags);		\
-	(dst) = (src);						\
-	spin_unlock_irqrestore(&(ptp)->ptp_lock, flags);	\
-} while (0)
-#else
-#define BNXT_READ_TIME64(ptp, dst, src)		\
-	((dst) = READ_ONCE(src))
-#endif
-
 #define BNXT_PTP_INC_TX_AVAIL(ptp)		\
 do {						\
 	spin_lock_bh(&(ptp)->ptp_tx_lock);	\
-- 
2.43.5