[PATCH net-next v4 1/2] net: dsa: yt921x: Fix MIB overflow wraparound routine

David Yang
2026-01-08T00:43:26Z

Reported by the following Smatch static checker warning:

drivers/net/dsa/yt921x.c:702 yt921x_read_mib()
warn: was expecting a 64 bit value instead of '(~0)'

Fixes: 186623f4aa72 ("net: dsa: yt921x: Add support for Motorcomm YT921x")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/netdev/aPsjYKQMzpY0nSXm@stanley.mountain/
Suggested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: David Yang <mmyangfl@gmail.com>
---
drivers/net/dsa/yt921x.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/net/dsa/yt921x.c b/drivers/net/dsa/yt921x.c
index 0b3df732c0d1..5e4e8093ba16 100644
--- a/drivers/net/dsa/yt921x.c
+++ b/drivers/net/dsa/yt921x.c
@@ -682,21 +682,22 @@ static int yt921x_read_mib(struct yt921x_priv *priv, int port)
const struct yt921x_mib_desc *desc = &yt921x_mib_descs[i];
u32 reg = YT921X_MIBn_DATA0(port) + desc->offset;
u64 *valp = &((u64 *)mib)[i];
- u64 val = *valp;
u32 val0;
- u32 val1;
+ u64 val;

res = yt921x_reg_read(priv, reg, &val0);
if (res)
break;

if (desc->size <= 1) {
- if (val < (u32)val)
- /* overflow */
- val += (u64)U32_MAX + 1;
- val &= ~U32_MAX;
- val |= val0;
+ u64 old_val = *valp;
+
+ val = (old_val & ~(u64)U32_MAX) | val0;
+ if (val < old_val)
+ val += 1ull << 32;
} else {
+ u32 val1;
+
res = yt921x_reg_read(priv, reg + 4, &val1);
if (res)
break;
--
2.51.0