netdev - RE: [PATCH net-next v5 1/2] qed: Add infrastructure for PTP support

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Date:   Mon, 13 Feb 2017 21:51:08 +0000
From:   "Mintz, Yuval" <Yuval.Mintz@...ium.com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Kalluru, Sudarsana" <Sudarsana.Kalluru@...ium.com>
Subject: RE: [PATCH net-next v5 1/2] qed: Add infrastructure for PTP support

> > +static int qed_ptp_hw_adjfreq(struct qed_dev *cdev, s32 ppb) {
> > +	struct qed_hwfn *p_hwfn = QED_LEADING_HWFN(cdev);
> > +	struct qed_ptt *p_ptt = p_hwfn->p_ptp_ptt;
> > +	int drift_dir, best_val, best_period;
> > +	s64 period, dif, dif2;
> > +	u32 drift_ctr_cfg = 0;
> > +	s64 best_dif, val;
> > +	u32 drift_state;
> > +
> > +	best_dif = ppb;

Crap. Apparently I've sent my early draft.

'best_dif' is the culprit for the odd results [not the -8].
In the previous calculation it was the theoretical upper-bound,
now it should be an unreachable number instead [7000000000].

> > +	best_period = 2;
> > +	best_val = 0;
> > +	drift_dir = 1;
> > +
> > +	if (ppb < 0) {
> > +		ppb = -ppb;
> > +		drift_dir = 0;
> > +	}
> > +
> > +	if (ppb == 0) {
> > +		/* No clock adjustment required */
> > +		best_val = 0;
> > +		best_period = 0xFFFFFFF;
> > +	} else {
> > +		/* Adjustment value is up to +/-7ns, find an optimal value in
> > +		 * this range.
> > +		 */
> > +		for (val = 7; val > 0; val++) {
> 
> This is an endless loop. ------------- ^^^^^

And this, obviously...

> 
> Besides that, this code returns some very strange values.  For example, for
> ppb = 100106, 100107, and 100108.  Also ppb = 1...8 all return 0/40.
> 
> Trouble with the -= 8?
> 
> I can only recommend plotting all of the raw errors and also average
> (RMS) error over the nominal interval ppb = 1...500000.
> 

I'll send the corrected v6 tomorrow. Sorry about this one.