[PATCH net-next v4 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. Lower 8 bits of the cached value will be used to check for
roll-over while extending to full 48 bits.
This change makes 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 | 18 +++---------------
 2 files changed, 7 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..820c7e83e586 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 >> BNXT_HI_TIMER_SHIFT));
 	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 >> BNXT_HI_TIMER_SHIFT));
 }
 
 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) << BNXT_HI_TIMER_SHIFT);
 	*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 >> BNXT_HI_TIMER_SHIFT));
 		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..3ac5cbc1c5c4 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h
@@ -21,6 +21,7 @@
 #define BNXT_DEVCLK_FREQ	1000000
 #define BNXT_LO_TIMER_MASK	0x0000ffffffffUL
 #define BNXT_HI_TIMER_MASK	0xffff00000000UL
+#define BNXT_HI_TIMER_SHIFT	24
 
 #define BNXT_PTP_DFLT_TX_TMO	1000 /* ms */
 #define BNXT_PTP_QTS_TIMEOUT	1000
@@ -106,10 +107,11 @@ 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;
+	/* cache of upper 24 bits of cyclecoutner. 8 bits are used to check for roll-over */
+	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 +147,6 @@ 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