netdev - Re: [PATCH 4/4] net: dsa: mv88e6xxx: add PTP support for MV88E6250 family

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Date:   Tue, 30 Jul 2019 18:20:00 +0200
From:   Hubert Feurstein <h.feurstein@...il.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Subject: Re: [PATCH 4/4] net: dsa: mv88e6xxx: add PTP support for MV88E6250 family

Hi Richard,

thank you for your comments.

Am Di., 30. Juli 2019 um 18:00 Uhr schrieb Richard Cochran
<richardcochran@...il.com>:
[...]
> > -/* Raw timestamps are in units of 8-ns clock periods. */
> > -#define CC_SHIFT     28
> > -#define CC_MULT              (8 << CC_SHIFT)
> > -#define CC_MULT_NUM  (1 << 9)
> > -#define CC_MULT_DEM  15625ULL
> > +/* The adjfine API clamps ppb between [-32,768,000, 32,768,000], and
>
> That is not true.
>
> > + * therefore scaled_ppm between [-2,147,483,648, 2,147,483,647].
> > + * Set the maximum supported ppb to a round value smaller than the maximum.
> > + *
> > + * Percentually speaking, this is a +/- 0.032x adjustment of the
> > + * free-running counter (0.968x to 1.032x).
> > + */
> > +#define MV88E6XXX_MAX_ADJ_PPB        32000000
>
> I had set an arbitrary limit of 1000 ppm.  I can't really see any
> point in raising the limit.
>
> > +/* Family MV88E6250:
> > + * Raw timestamps are in units of 10-ns clock periods.
> > + *
> > + * clkadj = scaled_ppm * 10*2^28 / (10^6 * 2^16)
> > + * simplifies to
> > + * clkadj = scaled_ppm * 2^7 / 5^5
> > + */
> > +#define MV88E6250_CC_SHIFT   28
> > +#define MV88E6250_CC_MULT    (10 << MV88E6250_CC_SHIFT)
> > +#define MV88E6250_CC_MULT_NUM        (1 << 7)
> > +#define MV88E6250_CC_MULT_DEM        3125ULL
> > +
> > +/* Other families:
> > + * Raw timestamps are in units of 8-ns clock periods.
> > + *
> > + * clkadj = scaled_ppm * 8*2^28 / (10^6 * 2^16)
> > + * simplifies to
> > + * clkadj = scaled_ppm * 2^9 / 5^6
> > + */
> > +#define MV88E6XXX_CC_SHIFT   28
> > +#define MV88E6XXX_CC_MULT    (8 << MV88E6XXX_CC_SHIFT)
> > +#define MV88E6XXX_CC_MULT_NUM        (1 << 9)
> > +#define MV88E6XXX_CC_MULT_DEM        15625ULL
> >
> >  #define TAI_EVENT_WORK_INTERVAL msecs_to_jiffies(100)
> >
> > @@ -179,24 +206,14 @@ static void mv88e6352_tai_event_work(struct work_struct *ugly)
> >  static int mv88e6xxx_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
> >  {
> >       struct mv88e6xxx_chip *chip = ptp_to_chip(ptp);
> > -     int neg_adj = 0;
> > -     u32 diff, mult;
> > -     u64 adj;
> > +     s64 adj;
> >
> > -     if (scaled_ppm < 0) {
> > -             neg_adj = 1;
> > -             scaled_ppm = -scaled_ppm;
> > -     }
>
> Please don't re-write this logic.  It is written like that for a reason.
I used the sja1105_ptp.c as a reference. So it is also wrong there.

Hubert