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ptp: Introduce a high resolution frequency adjustment method.

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The internal PTP Hardware Clock (PHC) interface limits the resolution for
frequency adjustments to one part per billion.  However, some hardware
devices allow finer adjustment, and making use of the increased resolution
improves synchronization measurably on such devices.

This patch adds an alternative method that allows finer frequency tuning
by passing the scaled ppm value to PHC drivers.  This value comes from
user space, and it has a resolution of about 0.015 ppb.  We also deprecate
the older method, anticipating its removal once existing drivers have been
converted over.

Signed-off-by: Richard Cochran <[email protected]>
Suggested-by: Ulrik De Bie <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Richard Cochran 2016-11-08 22:49:16 +01:00 • committed by David S. Miller
commit d8d2635419
2 changed files with 12 additions and 1 deletions
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5
drivers/ptp/ptp_clock.c
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@ -153,7 +153,10 @@ static int ptp_clock_adjtime(struct posix_clock *pc, struct timex *tx)
s32 ppb = scaled_ppm_to_ppb(tx->freq);
if (ppb > ops->max_adj || ppb < -ops->max_adj)
return -ERANGE;
err = ops->adjfreq(ops, ppb);
if (ops->adjfine)
err = ops->adjfine(ops, tx->freq);
else
err = ops->adjfreq(ops, ppb);
ptp->dialed_frequency = tx->freq;
} else if (tx->modes == 0) {
tx->freq = ptp->dialed_frequency;