[PATCH net] net: dsa: qca8k: propagate MDIO errors

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

qca8k_mii_write32() ignores errors from both 16-bit half-word writes.
Its callers (register writes and read-modify-write helpers) then return
the earlier successful page selection or read result, incorrectly
reporting success even when writing the switch register failed.

Propagate write errors from both the low and high half-words through the
regmap paths and internal MDIO master transactions. Attempt to clear
MASTER_EN even if a transaction fails, preserving the initial error, and
report a cleanup failure if the transaction itself succeeded. Preserve
the existing Ethernet-to-MDIO fallback order.

Propagate read errors through the internal and legacy MDIO bus callbacks
instead of masking them as 0xffff. Returning 0xffff causes PHY
read-modify-write callers to treat the failed read as valid register
data, which can corrupt unrelated bits on writeback.

Stop polling when reading the MDIO busy status fails, and return the
error immediately. Because the read helper clears its output on failure,
checking only the BUSY bit mistakes an unsuccessful read for transaction
completion.

Fixes: 6b93fb46480a ("net-next: dsa: add new driver for qca8xxx family")

Signed-off-by: Yongzhao Chen <yongzhao.derek@gmail.com>
Assisted-by: LLM
---
 drivers/net/dsa/qca/qca8k-8xxx.c | 51 ++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 23 deletions(-)

diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
index 60f2a615a..f9e2eb0b9 100644
--- a/drivers/net/dsa/qca/qca8k-8xxx.c
+++ b/drivers/net/dsa/qca/qca8k-8xxx.c
@@ -129,13 +129,16 @@ qca8k_mii_read32(struct mii_bus *bus, int phy_id, u32 regnum, u32 *val)
 	return ret;
 }
 
-static void
+static int
 qca8k_mii_write32(struct mii_bus *bus, int phy_id, u32 regnum, u32 val)
 {
-	if (qca8k_mii_write_lo(bus, phy_id, regnum, val) < 0)
-		return;
+	int ret;
+
+	ret = qca8k_mii_write_lo(bus, phy_id, regnum, val);
+	if (ret < 0)
+		return ret;
 
-	qca8k_mii_write_hi(bus, phy_id, regnum + 1, val);
+	return qca8k_mii_write_hi(bus, phy_id, regnum + 1, val);
 }
 
 static int
@@ -462,7 +465,7 @@ qca8k_write_mii(struct qca8k_priv *priv, uint32_t reg, uint32_t val)
 	if (ret < 0)
 		goto exit;
 
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	ret = qca8k_mii_write32(bus, 0x10 | r2, r1, val);
 
 exit:
 	mutex_unlock(&bus->mdio_lock);
@@ -492,7 +495,7 @@ qca8k_regmap_update_bits_mii(struct qca8k_priv *priv, uint32_t reg,
 
 	val &= ~mask;
 	val |= write_val;
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	ret = qca8k_mii_write32(bus, 0x10 | r2, r1, val);
 
 exit:
 	mutex_unlock(&bus->mdio_lock);
@@ -799,14 +802,13 @@ qca8k_mdio_busy_wait(struct mii_bus *bus, u32 reg, u32 mask)
 
 	qca8k_split_addr(reg, &r1, &r2, &page);
 
-	ret = read_poll_timeout(qca8k_mii_read_hi, ret1, !(val & mask), 0,
+	ret = read_poll_timeout(qca8k_mii_read_hi, ret1,
+				ret1 < 0 || !(val & mask), 0,
 				QCA8K_BUSY_WAIT_TIMEOUT * USEC_PER_MSEC, false,
 				bus, 0x10 | r2, r1 + 1, &val);
 
-	/* Check if qca8k_read has failed for a different reason
-	 * before returnting -ETIMEDOUT
-	 */
-	if (ret < 0 && ret1 < 0)
+	/* Preserve an MDIO read error instead of treating it as ready. */
+	if (ret1 < 0)
 		return ret1;
 
 	return ret;
@@ -818,7 +820,7 @@ qca8k_mdio_write(struct qca8k_priv *priv, int phy, int regnum, u16 data)
 	struct mii_bus *bus = priv->bus;
 	u16 r1, r2, page;
 	u32 val;
-	int ret;
+	int ret, ret1;
 
 	if (regnum >= QCA8K_MDIO_MASTER_MAX_REG)
 		return -EINVAL;
@@ -836,14 +838,18 @@ qca8k_mdio_write(struct qca8k_priv *priv, int phy, int regnum, u16 data)
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	ret = qca8k_mii_write32(bus, 0x10 | r2, r1, val);
+	if (ret < 0)
+		goto exit;
 
 	ret = qca8k_mdio_busy_wait(bus, QCA8K_MDIO_MASTER_CTRL,
 				   QCA8K_MDIO_MASTER_BUSY);
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, 0);
+	ret1 = qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, 0);
+	if (!ret)
+		ret = ret1;
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -856,7 +862,7 @@ qca8k_mdio_read(struct qca8k_priv *priv, int phy, int regnum)
 	struct mii_bus *bus = priv->bus;
 	u16 r1, r2, page;
 	u32 val;
-	int ret;
+	int ret, ret1;
 
 	if (regnum >= QCA8K_MDIO_MASTER_MAX_REG)
 		return -EINVAL;
@@ -873,7 +879,9 @@ qca8k_mdio_read(struct qca8k_priv *priv, int phy, int regnum)
 	if (ret)
 		goto exit;
 
-	qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, val);
+	ret = qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, val);
+	if (ret < 0)
+		goto exit;
 
 	ret = qca8k_mdio_busy_wait(bus, QCA8K_MDIO_MASTER_CTRL,
 				   QCA8K_MDIO_MASTER_BUSY);
@@ -884,7 +892,9 @@ qca8k_mdio_read(struct qca8k_priv *priv, int phy, int regnum)
 
 exit:
 	/* even if the busy_wait timeouts try to clear the MASTER_EN */
-	qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, 0);
+	ret1 = qca8k_mii_write_hi(bus, 0x10 | r2, r1 + 1, 0);
+	if (!ret)
+		ret = ret1;
 
 	mutex_unlock(&bus->mdio_lock);
 
@@ -919,12 +929,7 @@ qca8k_internal_mdio_read(struct mii_bus *slave_bus, int phy, int regnum)
 	if (ret >= 0)
 		return ret;
 
-	ret = qca8k_mdio_read(priv, phy, regnum);
-
-	if (ret < 0)
-		return 0xffff;
-
-	return ret;
+	return qca8k_mdio_read(priv, phy, regnum);
 }
 
 static int
-- 
2.43.0