[PATCH net v2] net: dsa: sja1105: round up PTP perout pin duration

[Aleksandrova Alyona <aga@itb.spb.ru>]

pin_duration is converted from the user-provided period to SJA1105
clock ticks and is later passed as the cycle_time argument to
future_base_time().

Very small period values may become zero after the conversion,
which can lead to a division by zero in future_base_time().

Round zero pin_duration up to 1 tick so that the smallest unsupported
periods use the minimum non-zero hardware duration instead of passing
zero to future_base_time().

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 747e5eb31d59 ("net: dsa: sja1105: configure the PTP_CLK pin as EXT_TS or PER_OUT")
Signed-off-by: Aleksandrova Alyona <aga@itb.spb.ru>
---
v2:
- Round up zero pin_duration to 1 instead of rejecting it, as suggested
  by Andrew Lunn.

 drivers/net/dsa/sja1105/sja1105_ptp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/sja1105/sja1105_ptp.c b/drivers/net/dsa/sja1105/sja1105_ptp.c
index a7d41e781398..afb11690c217 100644
--- a/drivers/net/dsa/sja1105/sja1105_ptp.c
+++ b/drivers/net/dsa/sja1105/sja1105_ptp.c
@@ -755,7 +755,7 @@ static int sja1105_per_out_enable(struct sja1105_private *priv,
 		 * 2 edges on PTP_CLK. So check for truncation which happens
 		 * at periods larger than around 68.7 seconds.
 		 */
-		pin_duration = ns_to_sja1105_ticks(pin_duration / 2);
+		pin_duration = max_t(u64, ns_to_sja1105_ticks(pin_duration / 2), 1);
 		if (pin_duration > U32_MAX) {
 			rc = -ERANGE;
 			goto out;
-- 
2.26.2