[PATCH net 1/3] net: dsa: mt7530: check bus->read() errors in the MDIO regmap backend

[Daniel Golle]

bus->read() returns a negative errno on failure, but
mt7530_regmap_read() assigns it to a u16, truncating e.g. -ETIMEDOUT
into 0xff92, and returns success. The garbage word is then consumed as
register data, and read-modify-write cycles write it back to the
switch. Check both reads and propagate their errors.

The same defect existed in mt7530_mii_read() since the driver was
introduced and moved into the regmap backend unchanged.

Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
---
 drivers/net/dsa/mt7530-mdio.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mt7530-mdio.c b/drivers/net/dsa/mt7530-mdio.c
index 11ea924a9f35..784dd58a7158 100644
--- a/drivers/net/dsa/mt7530-mdio.c
+++ b/drivers/net/dsa/mt7530-mdio.c
@@ -55,8 +55,15 @@ mt7530_regmap_read(void *context, unsigned int reg, unsigned int *val)
 	if (ret < 0)
 		return ret;
 
-	lo = bus->read(bus, priv->mdiodev->addr, r);
-	hi = bus->read(bus, priv->mdiodev->addr, 0x10);
+	ret = bus->read(bus, priv->mdiodev->addr, r);
+	if (ret < 0)
+		return ret;
+	lo = ret;
+
+	ret = bus->read(bus, priv->mdiodev->addr, 0x10);
+	if (ret < 0)
+		return ret;
+	hi = ret;
 
 	*val = (hi << 16) | (lo & 0xffff);
 
-- 
2.55.0