[PATCH net-next] net: lan966x: Fix lan966x_ifh_get

[Horatiu Vultur]

>From time to time, it was observed that the nanosecond part of the
received timestamp, which is extracted from the IFH, it was actually
bigger than 1 second. So then when actually calculating the full
received timestamp, based on the nanosecond part from IFH and the second
part which is read from HW, it was actually wrong.

The issue seems to be inside the function lan966x_ifh_get, which
extracts information from an IFH(which is an byte array) and returns the
value in a u64. When extracting the timestamp value from the IFH, which
starts at bit 192 and have the size of 32 bits, then if the most
significant bit was set in the timestamp, then this bit was extended
then the return value became 0xffffffff... . To fix this, make sure to
clear all the other bits before returning the value.

Fixes: fd7627833ddf ("net: lan966x: Stop using packing library")
Signed-off-by: Horatiu Vultur <horatiu.vultur@xxxxxxxxxxxxx>
---
 drivers/net/ethernet/microchip/lan966x/lan966x_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
index 80e2ea7e6ce8a..508e494dcc342 100644
--- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
+++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.c
@@ -608,6 +608,7 @@ static u64 lan966x_ifh_get(u8 *ifh, size_t pos, size_t length)
 			val |= (1 << i);
 	}
 
+	val &= GENMASK(length, 0);
 	return val;
 }
 
-- 
2.38.0