linux-kernel - [PATCH v1] ptp_qoriq: fix latency in ptp_qoriq

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Message-Id: <20230116102440.27189-1-nikhil.gupta@nxp.com>
Date:   Mon, 16 Jan 2023 15:54:40 +0530
From:   nikhil.gupta@....com
To:     linux-arm-kernel@...ts.infradead.org,
        Yangbo Lu <yangbo.lu@....com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     vakul.garg@....com, rajan.gupta@....com, richardcochran@...il.com,
        Nikhil Gupta <nikhil.gupta@....com>
Subject: [PATCH v1] ptp_qoriq: fix latency in ptp_qoriq_adjtime() operation.

From: Nikhil Gupta <nikhil.gupta@....com>

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 keeps
incrementing, it leads to latency.
The tmr_offset register (which is added to TMR_CNT_H/L register
gives the current time) must be programmed with the delta
nanoseconds.

Signed-off-by: Nikhil Gupta <nikhil.gupta@....com>
Reviewed-by: Yangbo Lu <yangbo.lu@....com>
---
 drivers/ptp/ptp_qoriq.c | 35 ++++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/drivers/ptp/ptp_qoriq.c b/drivers/ptp/ptp_qoriq.c
index 08f4cf0ad9e3..69fa77b99b45 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;
@@ -212,10 +237,9 @@ int ptp_qoriq_adjtime(struct ptp_clock_info *ptp, s64 delta)
 	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 = tmr_offset_read(ptp_qoriq);
 	now += delta;
-	tmr_cnt_write(ptp_qoriq, now);
+	tmr_offset_write(ptp_qoriq, now);
 	set_fipers(ptp_qoriq);
 
 	spin_unlock_irqrestore(&ptp_qoriq->lock, flags);
@@ -232,7 +256,7 @@ 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);
 
@@ -253,6 +277,7 @@ int ptp_qoriq_settime(struct ptp_clock_info *ptp,
 
 	spin_lock_irqsave(&ptp_qoriq->lock, flags);
 
+	tmr_offset_write(ptp_qoriq, 0);
 	tmr_cnt_write(ptp_qoriq, ns);
 	set_fipers(ptp_qoriq);
 
-- 
2.17.1