dsa: Fix conversion from host device to mii bus

Commit b4d2394d01bc ("dsa: Replace mii_bus with a generic host device")
replaces mii_bus with a generic host_dev, and introduces
dsa_host_dev_to_mii_bus() to support conversion from host_dev to mii_bus.
However, in some cases it uses to_mii_bus to perform that conversion.
Since host_dev is not the phy bus device but typically a platform device,
this fails and results in a crash with the affected drivers.

BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: [<ffffffff81781d35>] __mutex_lock_slowpath+0x75/0x100
PGD 406783067 PUD 406784067 PMD 0
Oops: 0002 [#1] SMP
...
Call Trace:
[<ffffffff810a538b>] ? pick_next_task_fair+0x61b/0x880
[<ffffffff81781de3>] mutex_lock+0x23/0x37
[<ffffffff81533244>] mdiobus_read+0x34/0x60
[<ffffffff8153b95a>] __mv88e6xxx_reg_read+0x8a/0xa0
[<ffffffff8153b9bc>] mv88e6xxx_reg_read+0x4c/0xa0

Fixes: b4d2394d01bc ("dsa: Replace mii_bus with a generic host device")
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 4 deletions

diff --git a/drivers/net/dsa/mv88e6060.c b/drivers/net/dsa/mv88e6060.c
index 776e965dc9f4..05b0ca3bf71d 100644
--- a/drivers/net/dsa/mv88e6060.c
+++ b/drivers/net/dsa/mv88e6060.c
@@ -21,8 +21,12 @@
 
 static int reg_read(struct dsa_switch *ds, int addr, int reg)
 {
-        return mdiobus_read(to_mii_bus(ds->master_dev),
-                            ds->pd->sw_addr + addr, reg);
+        struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);
+
+        if (bus == NULL)
+                return -EINVAL;
+
+        return mdiobus_read(bus, ds->pd->sw_addr + addr, reg);
 }
 
 #define REG_READ(addr, reg)                                     \
@@ -38,8 +42,12 @@ static int reg_read(struct dsa_switch *ds, int addr, int reg)
 
 static int reg_write(struct dsa_switch *ds, int addr, int reg, u16 val)
 {
-        return mdiobus_write(to_mii_bus(ds->master_dev),
-                             ds->pd->sw_addr + addr, reg, val);
+        struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);
+
+        if (bus == NULL)
+                return -EINVAL;
+
+        return mdiobus_write(bus, ds->pd->sw_addr + addr, reg, val);
 }
 
 #define REG_WRITE(addr, reg, val)                               \