[PATCH net v2 3/3] net: dsa: qca8k: fail mgmt Ethernet MDIO access on busy wait errors

[Yongzhao Chen <yongzhao.derek@gmail.com>]

qca8k_phy_eth_command() polls MASTER_CTRL over management Ethernet until
BUSY clears, but only bails out when the poll timed out and the last
poll request also failed. If every request succeeds while BUSY stays
set, the -ETIMEDOUT is dropped. A read then returns MASTER_CTRL data
from a transaction that has not completed, and
qca8k_internal_mdio_read() does not fall back to the MDIO bus.

A failed poll request does not stop the loop either.
qca8k_phy_eth_busy_wait() leaves the value unchanged on failure, so the
BUSY test then uses the previous value, or an uninitialized one if the
first request fails.

Stop polling when a request fails and return the poll error or timeout.
The early return also leaked read_skb, which is only consumed when the
read request is sent; free it on this path.

Fixes: 2cd548566384 ("net: dsa: qca8k: add support for phy read/write with mgmt Ethernet")
Signed-off-by: Yongzhao Chen <yongzhao.derek@gmail.com>
Assisted-by: LLM
---
v2: new patch, addressing the Sashiko review of v1:
https://lore.kernel.org/netdev/179054715863.3145.10179961093285192493@kernel.org/

 drivers/net/dsa/qca/qca8k-8xxx.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index 00a70c7880e..420b375b8b0 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -728,12 +728,15 @@ qca8k_phy_eth_command(struct qca8k_priv *priv, bool read, int phy,
 	}
 
 	ret = read_poll_timeout(qca8k_phy_eth_busy_wait, ret1,
-				!(val & QCA8K_MDIO_MASTER_BUSY), 0,
+				ret1 < 0 || !(val & QCA8K_MDIO_MASTER_BUSY), 0,
 				QCA8K_BUSY_WAIT_TIMEOUT * USEC_PER_MSEC, false,
 				mgmt_eth_data, read_skb, &val);
 
-	if (ret < 0 && ret1 < 0) {
+	if (ret1 < 0)
 		ret = ret1;
+
+	if (ret < 0) {
+		kfree_skb(read_skb);
 		goto exit;
 	}
 
-- 
2.43.0