Re: [PATCH] ptp_qoriq: fix overflow in ptp_qoriq_adjfine() u64 calcalation

On Thu, Mar 25, 2021 at 03:23:07AM -0700, Guenter Roeck wrote:

On Tue, Mar 23, 2021 at 04:02:29PM +0800, Yangbo Lu wrote:

quoted

Current calculation for diff of TMR_ADD register value may have
64-bit overflow in this code line, when long type scaled_ppm is
large.

adj *= scaled_ppm;

This patch is to resolve it by using mul_u64_u64_div_u64().

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
---
 drivers/ptp/ptp_qoriq.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/ptp/ptp_qoriq.c b/drivers/ptp/ptp_qoriq.c
index 68beb1bd07c0..f7f220700cb5 100644
--- a/drivers/ptp/ptp_qoriq.c
+++ b/drivers/ptp/ptp_qoriq.c

@@ -189,15 +189,16 @@ int ptp_qoriq_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
 	tmr_add = ptp_qoriq->tmr_add;
 	adj = tmr_add;
 
-	/* calculate diff as adj*(scaled_ppm/65536)/1000000
-	 * and round() to the nearest integer
+	/*
+	 * Calculate diff and round() to the nearest integer
+	 *
+	 * diff = adj * (ppb / 1000000000)
+	 *      = adj * scaled_ppm / 65536000000
 	 */
-	adj *= scaled_ppm;
-	diff = div_u64(adj, 8000000);
-	diff = (diff >> 13) + ((diff >> 12) & 1);
+	diff = mul_u64_u64_div_u64(adj, scaled_ppm, 32768000000);

mul_u64_u64_div_u64() is not exported. As result, every build with
CONFIG_PTP_1588_CLOCK_QORIQ=m (ie every allmodconfig build) fails with:

ERROR: modpost: "mul_u64_u64_div_u64" [drivers/ptp/ptp-qoriq.ko] undefined!

or a similar error.

Ah, never mind. I see this is fixed in mainline (export added).
I see the problem in pending-fixes and in next-20210325.

Sorry for the noise.

Guenter