RE: [PATCH] ptp_qoriq: fix latency in ptp_qoriq_adjtime() operation.

[Nikhil Gupta]

++ Richard Cochran

-----Original Message-----
From: nikhil.gupta@xxxxxxx <nikhil.gupta@xxxxxxx> 
Sent: Tuesday, January 10, 2023 5:00 PM
To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Y.B. Lu <yangbo.lu@xxxxxxx>; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Cc: Vakul Garg <vakul.garg@xxxxxxx>; Rajan Gupta <rajan.gupta@xxxxxxx>; Nikhil Gupta <nikhil.gupta@xxxxxxx>
Subject: [PATCH] ptp_qoriq: fix latency in ptp_qoriq_adjtime() operation.

From: Nikhil Gupta <nikhil.gupta@xxxxxxx>

1588 driver loses about 1us in adjtime operation at PTP slave.
This is because adjtime operation uses a slow non-atomic tmr_cnt_read() followed by tmr_cnt_write() operation.
In the above sequence, since the timer counter operation loses about 1us.
Instead, tmr_offset register should be programmed with the delta nanoseconds This won't lead to timer counter stopping and losing time while tmr_cnt_write() is being done.
This Patch adds api for tmr_offset_read/write to program the delta nanoseconds in the Timer offset Register.

Signed-off-by: Nikhil Gupta <nikhil.gupta@xxxxxxx>
Reviewed-by: Yangbo Lu <yangbo.lu@xxxxxxx>
---
 drivers/ptp/ptp_qoriq.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/drivers/ptp/ptp_qoriq.c b/drivers/ptp/ptp_qoriq.c index 08f4cf0ad9e3..5b6ea6d590be 100644
--- a/drivers/ptp/ptp_qoriq.c
+++ b/drivers/ptp/ptp_qoriq.c
@@ -48,6 +48,29 @@ static void tmr_cnt_write(struct ptp_qoriq *ptp_qoriq, u64 ns)
 	ptp_qoriq->write(&regs->ctrl_regs->tmr_cnt_h, hi);  }
 
+static void tmr_offset_write(struct ptp_qoriq *ptp_qoriq, u64 delta_ns) 
+{
+	struct ptp_qoriq_registers *regs = &ptp_qoriq->regs;
+	u32 hi = delta_ns >> 32;
+	u32 lo = delta_ns & 0xffffffff;
+
+	ptp_qoriq->write(&regs->ctrl_regs->tmroff_l, lo);
+	ptp_qoriq->write(&regs->ctrl_regs->tmroff_h, hi); }
+
+static u64 tmr_offset_read(struct ptp_qoriq *ptp_qoriq) {
+	struct ptp_qoriq_registers *regs = &ptp_qoriq->regs;
+	u64 ns;
+	u32 lo, hi;
+
+	lo = ptp_qoriq->read(&regs->ctrl_regs->tmroff_l);
+	hi = ptp_qoriq->read(&regs->ctrl_regs->tmroff_h);
+	ns = ((u64) hi) << 32;
+	ns |= lo;
+	return ns;
+}
+
 /* Caller must hold ptp_qoriq->lock. */  static void set_alarm(struct ptp_qoriq *ptp_qoriq)  { @@ -55,7 +78,9 @@ static void set_alarm(struct ptp_qoriq *ptp_qoriq)
 	u64 ns;
 	u32 lo, hi;
 
-	ns = tmr_cnt_read(ptp_qoriq) + 1500000000ULL;
+	ns = tmr_cnt_read(ptp_qoriq) + tmr_offset_read(ptp_qoriq)
+				     + 1500000000ULL;
+
 	ns = div_u64(ns, 1000000000UL) * 1000000000ULL;
 	ns -= ptp_qoriq->tclk_period;
 	hi = ns >> 32;
@@ -207,15 +232,12 @@ EXPORT_SYMBOL_GPL(ptp_qoriq_adjfine);
 
 int ptp_qoriq_adjtime(struct ptp_clock_info *ptp, s64 delta)  {
-	s64 now;
 	unsigned long flags;
 	struct ptp_qoriq *ptp_qoriq = container_of(ptp, struct ptp_qoriq, caps);
 
 	spin_lock_irqsave(&ptp_qoriq->lock, flags);
 
-	now = tmr_cnt_read(ptp_qoriq);
-	now += delta;
-	tmr_cnt_write(ptp_qoriq, now);
+	tmr_offset_write(ptp_qoriq, delta);
 	set_fipers(ptp_qoriq);
 
 	spin_unlock_irqrestore(&ptp_qoriq->lock, flags); @@ -232,7 +254,7 @@ int ptp_qoriq_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
 
 	spin_lock_irqsave(&ptp_qoriq->lock, flags);
 
-	ns = tmr_cnt_read(ptp_qoriq);
+	ns = tmr_cnt_read(ptp_qoriq) + tmr_offset_read(ptp_qoriq);
 
 	spin_unlock_irqrestore(&ptp_qoriq->lock, flags);
 
@@ -251,6 +273,8 @@ int ptp_qoriq_settime(struct ptp_clock_info *ptp,
 
 	ns = timespec64_to_ns(ts);
 
+	tmr_offset_write(ptp_qoriq, 0);
+
 	spin_lock_irqsave(&ptp_qoriq->lock, flags);
 
 	tmr_cnt_write(ptp_qoriq, ns);
--
2.17.1