Subject: Re: [RFC PATCH 04/10] net: dsa: mv88e6xxx: expose switch time as a PTP hardware clock

From: Richard Cochran <[email-masked]>
Date: Fri, 9 Feb 2018 12:33:36 -0800

On Sat, Feb 03, 2018 at 10:40:08PM +0100, Andrew Lunn wrote:
> +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;
> +
> +	if (scaled_ppm < 0) {
> +		neg_adj = 1;
> +		scaled_ppm = -scaled_ppm;
> +	}
> +	mult = CC_MULT;
> +	adj = scaled_ppm * CC_MULT_NUM;
              ^^^^^^^^^^^^^^^^^^^^^^^^
This easily overflows on 32 bit platforms.  My bad.  Fix below...

> +	diff = div_u64(adj, CC_MULT_DEM);
> +
> +	mutex_lock(&chip->reg_lock);
> +
> +	timecounter_read(&chip->tstamp_tc);
> +	chip->tstamp_cc.mult = neg_adj ? mult - diff : mult + diff;
> +
> +	mutex_unlock(&chip->reg_lock);
> +
> +	return 0;
> +}

Thanks,
Richard

---
diff --git a/drivers/net/dsa/mv88e6xxx/ptp.c b/drivers/net/dsa/mv88e6xxx/ptp.c
index 92f318743bd4..bd85e2c390e1 100644
--- a/drivers/net/dsa/mv88e6xxx/ptp.c
+++ b/drivers/net/dsa/mv88e6xxx/ptp.c
@@ -177,7 +177,8 @@ static int mv88e6xxx_ptp_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
 		scaled_ppm = -scaled_ppm;
 	}
 	mult = CC_MULT;
-	adj = scaled_ppm * CC_MULT_NUM;
+	adj = CC_MULT_NUM;
+	adj *= scaled_ppm;
 	diff = div_u64(adj, CC_MULT_DEM);
 
 	mutex_lock(&chip->reg_lock);