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Message-ID: <20230111210856.745ef17c@kernel.org>
Date: Wed, 11 Jan 2023 21:08:56 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: nikhil.gupta@....com
Cc: linux-arm-kernel@...ts.infradead.org,
Yangbo Lu <yangbo.lu@....com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, vakul.garg@....com,
rajan.gupta@....com
Subject: Re: [PATCH] ptp_qoriq: fix latency in ptp_qoriq_adjtime()
operation.
please put [PATCH net-next] in the subject.
On Tue, 10 Jan 2023 17:00:24 +0530 nikhil.gupta@....com wrote:
> 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.
So far so good..
> In the above sequence, since the timer counter operation loses about 1us.
s/operation/keeps incrementing after the read/ ?
but frankly I don't think this sentence adds much
> Instead, tmr_offset register should be programmed with the delta
> nanoseconds
missing full stop at the end.
You should describe what the tmr_offset register does.
> This won't lead to timer counter stopping and losing time
> while tmr_cnt_write() is being done.
Stopping? The timer was actually stopping?
> This Patch adds api for tmr_offset_read/write to program the
Use imperative mood.
> delta nanoseconds in the Timer offset Register.
>
> Signed-off-by: Nikhil Gupta <nikhil.gupta@....com>
> Reviewed-by: Yangbo Lu <yangbo.lu@....com>
> ---
> 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(®s->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(®s->ctrl_regs->tmroff_l, lo);
> + ptp_qoriq->write(®s->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;
Order variable lines longest to shortest
> + lo = ptp_qoriq->read(®s->ctrl_regs->tmroff_l);
> + hi = ptp_qoriq->read(®s->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);
Writes to the offset register result in an add operation?
Or it's a pure write? What will the offset be after a sequence of
following adjtime() calls:
adjtime(+100);
adjtime(+100);
adjtime(+100);
?
> 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);
Shouldn't this be under the lock?
> spin_lock_irqsave(&ptp_qoriq->lock, flags);
>
> tmr_cnt_write(ptp_qoriq, ns);
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