RE: [net-next 14/14] ptp: xgbe: convert to .adjfine and adjust_by_scaled_ppm

["Keller, Jacob E" <jacob.e.keller@intel.com>]

> -----Original Message-----
> From: Tom Lendacky <thomas.lendacky@amd.com>
> Sent: Friday, August 19, 2022 9:05 AM
> To: Keller, Jacob E <jacob.e.keller@intel.com>; netdev@vger.kernel.org
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> Subject: Re: [net-next 14/14] ptp: xgbe: convert to .adjfine and
> adjust_by_scaled_ppm
> 
> On 8/18/22 17:27, Jacob Keller wrote:
> > The xgbe implementation of .adjfreq is implemented in terms of a
> > straight forward "base * ppb / 1 billion" calculation.
> >
> > Convert this driver to .adjfine and use adjust_by_scaled_ppm to calculate
> > the new addend value.
> >
> > Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
> > Cc: Tom Lendacky <thomas.lendacky@amd.com>
> > Cc: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
> > ---
> >
> > I do not have this hardware, and have only compile tested the change.
> >
> >   drivers/net/ethernet/amd/xgbe/xgbe-ptp.c | 20 ++++----------------
> >   1 file changed, 4 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
> b/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
> > index d06d260cf1e2..7051bd7cf6dc 100644
> > --- a/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
> > +++ b/drivers/net/ethernet/amd/xgbe/xgbe-ptp.c
> > @@ -134,27 +134,15 @@ static u64 xgbe_cc_read(const struct cyclecounter
> *cc)
> >   	return nsec;
> >   }
> >
> > -static int xgbe_adjfreq(struct ptp_clock_info *info, s32 delta)
> > +static int xgbe_adjfine(struct ptp_clock_info *info, long scaled_ppm)
> >   {
> >   	struct xgbe_prv_data *pdata = container_of(info,
> >   						   struct xgbe_prv_data,
> >   						   ptp_clock_info);
> >   	unsigned long flags;
> > -	u64 adjust;
> > -	u32 addend, diff;
> > -	unsigned int neg_adjust = 0;
> > +	u64 addend;
> >
> > -	if (delta < 0) {
> > -		neg_adjust = 1;
> > -		delta = -delta;
> > -	}
> > -
> > -	adjust = pdata->tstamp_addend;
> > -	adjust *= delta;
> > -	diff = div_u64(adjust, 1000000000UL);
> > -
> > -	addend = (neg_adjust) ? pdata->tstamp_addend - diff :
> > -				pdata->tstamp_addend + diff;
> > +	addend = adjust_by_scaled_ppm(pdata->tstamp_addend, scaled_ppm);
> 
> Since addend is now a u64, but the called function just afterwards,
> xgbe_update_tstamp_addend(), expects an unsigned int, won't this generate
> a compiler warning depending on the flags used?
> 

It doesn't seem to generate anything with W=1 or W=2 on my system. Its possible that the compiler can deduce that this won't overflow a u32?

We could add a check to ensure it doesn't overflow the u32 size?

> Thanks,
> Tom
> 
> >
> >   	spin_lock_irqsave(&pdata->tstamp_lock, flags);
> >
> > @@ -235,7 +223,7 @@ void xgbe_ptp_register(struct xgbe_prv_data *pdata)
> >   		 netdev_name(pdata->netdev));
> >   	info->owner = THIS_MODULE;
> >   	info->max_adj = pdata->ptpclk_rate;
> > -	info->adjfreq = xgbe_adjfreq;
> > +	info->adjfine = xgbe_adjfine;
> >   	info->adjtime = xgbe_adjtime;
> >   	info->gettime64 = xgbe_gettime;
> >   	info->settime64 = xgbe_settime;