[PATCH net v2 5/6] net: dsa: mt7530: check command register writes in fdb and vlan cmd

mt7530_fdb_cmd() and mt7530_vlan_cmd() start a command by writing the
BUSY bit to MT7530_ATC / MT7530_VTCR, then poll for it to clear.
mt7530_write() discards the write's return value, so a failed command
write leaves BUSY unset and the poll succeeds on its first read,
reporting a command that never ran as done -- returning stale FDB data
or silently dropping a VLAN table update.

Return mt7530_mii_write()'s error from mt7530_write() and check it in
both command helpers.

Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
Signed-off-by: Daniel Golle <[email protected]>
---
v2: new patch

 drivers/net/dsa/mt7530.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
index 69cee61564cb..c0437273270b 100644
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -185,14 +185,18 @@ mt7530_mii_read(struct mt7530_priv *priv, u32 reg)
 	return val;
 }
 
-static void
+static int
 mt7530_write(struct mt7530_priv *priv, u32 reg, u32 val)
 {
+	int ret;
+
 	mt7530_mutex_lock(priv);
 
-	mt7530_mii_write(priv, reg, val);
+	ret = mt7530_mii_write(priv, reg, val);
 
 	mt7530_mutex_unlock(priv);
+
+	return ret;
 }
 
 static u32
@@ -249,7 +253,9 @@ mt7530_fdb_cmd(struct mt7530_priv *priv, enum mt7530_fdb_cmd cmd, u32 *rsp)
 
 	/* Set the command operating upon the MAC address entries */
 	val = ATC_BUSY | ATC_MAT(0) | cmd;
-	mt7530_write(priv, MT7530_ATC, val);
+	ret = mt7530_write(priv, MT7530_ATC, val);
+	if (ret)
+		return ret;
 
 	mt7530_mutex_lock(priv);
 
@@ -1632,7 +1638,9 @@ mt7530_vlan_cmd(struct mt7530_priv *priv, enum mt7530_vlan_cmd cmd, u16 vid)
 	int ret;
 
 	val = VTCR_BUSY | VTCR_FUNC(cmd) | vid;
-	mt7530_write(priv, MT7530_VTCR, val);
+	ret = mt7530_write(priv, MT7530_VTCR, val);
+	if (ret)
+		return ret;
 
 	mt7530_mutex_lock(priv);
 
-- 
2.55.0