RE: [net-next, v3, 01/10] ptp: add ptp virtual clock driver framework

[Y.b. Lu]

Hi Richard,

> -----Original Message-----
> From: Richard Cochran <richardcochran@xxxxxxxxx>
> Sent: 2021年6月18日 1:33
> To: Y.b. Lu <yangbo.lu@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-kselftest@xxxxxxxxxxxxxxx; mptcp@xxxxxxxxxxxxxxx; David S . Miller
> <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Mat Martineau
> <mathew.j.martineau@xxxxxxxxxxxxxxx>; Matthieu Baerts
> <matthieu.baerts@xxxxxxxxxxxx>; Shuah Khan <shuah@xxxxxxxxxx>; Michal
> Kubecek <mkubecek@xxxxxxx>; Florian Fainelli <f.fainelli@xxxxxxxxx>;
> Andrew Lunn <andrew@xxxxxxx>; Rui Sousa <rui.sousa@xxxxxxx>; Sebastien
> Laveze <sebastien.laveze@xxxxxxx>
> Subject: Re: [net-next, v3, 01/10] ptp: add ptp virtual clock driver framework
> 
> On Tue, Jun 15, 2021 at 05:45:08PM +0800, Yangbo Lu wrote:
> > diff --git a/drivers/ptp/Makefile b/drivers/ptp/Makefile index
> > 8673d1743faa..3c6a905760e2 100644
> > --- a/drivers/ptp/Makefile
> > +++ b/drivers/ptp/Makefile
> > @@ -3,7 +3,7 @@
> >  # Makefile for PTP 1588 clock support.
> >  #
> >
> > -ptp-y					:= ptp_clock.o ptp_chardev.o ptp_sysfs.o
> > +ptp-y					:= ptp_clock.o ptp_vclock.o ptp_chardev.o
> ptp_sysfs.o
> 
> Nit: Please place ptp_vclock.o at the end of the list.

Ok.

> 
> >  ptp_kvm-$(CONFIG_X86)			:= ptp_kvm_x86.o ptp_kvm_common.o
> >  ptp_kvm-$(CONFIG_HAVE_ARM_SMCCC)	:= ptp_kvm_arm.o
> ptp_kvm_common.o
> >  obj-$(CONFIG_PTP_1588_CLOCK)		+= ptp.o
> 
> > diff --git a/drivers/ptp/ptp_private.h b/drivers/ptp/ptp_private.h
> > index 6b97155148f1..3f388d63904c 100644
> > --- a/drivers/ptp/ptp_private.h
> > +++ b/drivers/ptp/ptp_private.h
> > @@ -48,6 +48,20 @@ struct ptp_clock {
> >  	struct kthread_delayed_work aux_work;  };
> >
> > +#define info_to_vclock(d) container_of((d), struct ptp_vclock, info)
> > +#define cc_to_vclock(d) container_of((d), struct ptp_vclock, cc)
> > +#define dw_to_vclock(d) container_of((d), struct ptp_vclock,
> > +refresh_work)
> > +
> > +struct ptp_vclock {
> > +	struct ptp_clock *pclock;
> > +	struct ptp_clock_info info;
> > +	struct ptp_clock *clock;
> > +	struct cyclecounter cc;
> > +	struct timecounter tc;
> > +	spinlock_t lock;	/* protects tc/cc */
> > +	struct delayed_work refresh_work;
> 
> Can we please have a kthread worker here instead of work?
> 
> Experience shows that plain work can be delayed for a long, long time on busy
> systems.
> 

I think do_aux_work callback could be utilized for ptp virtual clock, right?

> > +};
> > +
> >  /*
> >   * The function queue_cnt() is safe for readers to call without
> >   * holding q->lock. Readers use this function to verify that the
> > queue @@ -89,4 +103,6 @@ extern const struct attribute_group
> > *ptp_groups[];  int ptp_populate_pin_groups(struct ptp_clock *ptp);
> > void ptp_cleanup_pin_groups(struct ptp_clock *ptp);
> >
> > +struct ptp_vclock *ptp_vclock_register(struct ptp_clock *pclock);
> > +void ptp_vclock_unregister(struct ptp_vclock *vclock);
> >  #endif
> 
> > diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c new
> > file mode 100644 index 000000000000..b8f500677314
> > --- /dev/null
> > +++ b/drivers/ptp/ptp_vclock.c
> > @@ -0,0 +1,154 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * PTP virtual clock driver
> > + *
> > + * Copyright 2021 NXP
> > + */
> > +#include <linux/slab.h>
> > +#include "ptp_private.h"
> > +
> > +#define PTP_VCLOCK_CC_MULT		(1 << 31)
> > +#define PTP_VCLOCK_CC_SHIFT		31
> 
> These two are okay, but ...
> 
> > +#define PTP_VCLOCK_CC_MULT_NUM		(1 << 9)
> > +#define PTP_VCLOCK_CC_MULT_DEM		15625ULL
> 
> the similarity of naming is confusing for these two.  They are only used in
> the .adjfine method.  How about this?
> 
>   PTP_VCLOCK_FADJ_NUMERATOR, or even PTP_VCLOCK_FADJ_SHIFT (see
> below)
>   PTP_VCLOCK_FADJ_DENOMINATOR
> 
> > +#define PTP_VCLOCK_CC_REFRESH_INTERVAL	(HZ * 2)
> 
> Consider dropping CC from the name.
> PTP_VCLOCK_REFRESH_INTERVAL sounds good to me.
> 

Thanks. Will rename the MACROs per your suggestion.

> > +static int ptp_vclock_adjfine(struct ptp_clock_info *ptp, long
> > +scaled_ppm) {
> > +	struct ptp_vclock *vclock = info_to_vclock(ptp);
> > +	unsigned long flags;
> > +	s64 adj;
> > +
> > +	adj = (s64)scaled_ppm * PTP_VCLOCK_CC_MULT_NUM;
> 
> Rather than
> 
>     scaled_ppm * (1 << 9)
> 
> I suggest
> 
>     scaled_ppm << 9
> 
> instead.  I suppose a good compiler would replace the multiplication with a
> bit shift, but it never hurts to spell it out.

Ok.

> 
> > +	adj = div_s64(adj, PTP_VCLOCK_CC_MULT_DEM);
> > +
> > +	spin_lock_irqsave(&vclock->lock, flags);
> > +	timecounter_read(&vclock->tc);
> > +	vclock->cc.mult = PTP_VCLOCK_CC_MULT + adj;
> > +	spin_unlock_irqrestore(&vclock->lock, flags);
> > +
> > +	return 0;
> > +}
> 
> Thanks,
> Richard