[PATCH net-next RFC v2] net: dsa: mv88e6xxx: Correct check for empty list

[Simon Horman <horms@kernel.org>]

Since commit a3c53be55c95 ("net: dsa: mv88e6xxx: Support multiple MDIO
busses") mv88e6xxx_default_mdio_bus() has checked that the
return value of list_first_entry() is non-NULL.

This appears to be intended to guard against the list chip->mdios being
empty.  However, it is not the correct check as the implementation of
list_first_entry is not designed to return NULL for empty lists.

Instead, use list_first_entry() which does return NULL if the list is
empty.

Flagged by Smatch.
Compile tested only.

Signed-off-by: Simon Horman <horms@kernel.org>
---
Changes in v2:
- Use list_first_entry_or_null() instead of open-coding
  a condition on list_empty().
  Suggested by Dan Carpenter.
- Update commit message.
- Link to v1: https://lore.kernel.org/r/20240419-mv88e6xx-list_empty-v1-1-64fd6d1059a8@kernel.org
---
As discussed in v1, this is not being considered a fix
as it has been like this for a long time without any
reported problems.
---
 drivers/net/dsa/mv88e6xxx/chip.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index f29ef72a2f1d..fc6e2e3ab0f0 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -131,8 +131,8 @@ struct mii_bus *mv88e6xxx_default_mdio_bus(struct mv88e6xxx_chip *chip)
 {
 	struct mv88e6xxx_mdio_bus *mdio_bus;
 
-	mdio_bus = list_first_entry(&chip->mdios, struct mv88e6xxx_mdio_bus,
-				    list);
+	mdio_bus = list_first_entry_or_null(&chip->mdios,
+					    struct mv88e6xxx_mdio_bus, list);
 	if (!mdio_bus)
 		return NULL;