Messages in this thread Patch in this message | | | Date | Wed, 11 Jan 2023 21:08:56 -0800 | From | Jakub Kicinski <> | Subject | Re: [PATCH] ptp_qoriq: fix latency in ptp_qoriq_adjtime() operation. |
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please put [PATCH net-next] in the subject.
On Tue, 10 Jan 2023 17:00:24 +0530 nikhil.gupta@nxp.com wrote: > From: Nikhil Gupta <nikhil.gupta@nxp.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@nxp.com> > Reviewed-by: Yangbo Lu <yangbo.lu@nxp.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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