net: dsa: mv88e6xxx: assert SMI lock

It's easy to forget to lock the smi_mutex before calling the low-level
_mv88e6xxx_reg_{read,write}, so add a assert_smi_lock function in them.
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx.c

@@ -24,6 +24,16 @@
 #include <net/switchdev.h>
 #include "mv88e6xxx.h"
 
+static void assert_smi_lock(struct dsa_switch *ds)
+{
+	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
+
+	if (unlikely(!mutex_is_locked(&ps->smi_mutex))) {
+		dev_err(ds->master_dev, "SMI lock not held!\n");
+		dump_stack();
+	}
+}
+
 /* If the switch's ADDR[4:0] strap pins are strapped to zero, it will
  * use all 32 SMI bus addresses on its SMI bus, and all switch registers
  * will be directly accessible on some {device address,register address}
@@ -80,12 +90,13 @@ int __mv88e6xxx_reg_read(struct mii_bus *bus, int sw_addr, int addr, int reg)
 	return ret & 0xffff;
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_reg_read(struct dsa_switch *ds, int addr, int reg)
 {
 	struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);
 	int ret;
 
+	assert_smi_lock(ds);
+
 	if (bus == NULL)
 		return -EINVAL;
 
@@ -143,12 +154,13 @@ int __mv88e6xxx_reg_write(struct mii_bus *bus, int sw_addr, int addr,
 	return 0;
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_reg_write(struct dsa_switch *ds, int addr, int reg,
 				u16 val)
 {
 	struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);
 
+	assert_smi_lock(ds);
+
 	if (bus == NULL)
 		return -EINVAL;
 
@@ -204,7 +216,6 @@ int mv88e6xxx_set_addr_indirect(struct dsa_switch *ds, u8 *addr)
 	return 0;
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_phy_read(struct dsa_switch *ds, int addr, int regnum)
 {
 	if (addr >= 0)
@@ -212,7 +223,6 @@ static int _mv88e6xxx_phy_read(struct dsa_switch *ds, int addr, int regnum)
 	return 0xffff;
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_phy_write(struct dsa_switch *ds, int addr, int regnum,
 				u16 val)
 {
@@ -538,7 +548,6 @@ void mv88e6xxx_adjust_link(struct dsa_switch *ds, int port,
 	mutex_unlock(&ps->smi_mutex);
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_stats_wait(struct dsa_switch *ds)
 {
 	int ret;
@@ -553,7 +562,6 @@ static int _mv88e6xxx_stats_wait(struct dsa_switch *ds)
 	return -ETIMEDOUT;
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_stats_snapshot(struct dsa_switch *ds, int port)
 {
 	int ret;
@@ -576,7 +584,6 @@ static int _mv88e6xxx_stats_snapshot(struct dsa_switch *ds, int port)
 	return 0;
 }
 
-/* Must be called with SMI mutex held */
 static void _mv88e6xxx_stats_read(struct dsa_switch *ds, int stat, u32 *val)
 {
 	u32 _val;
@@ -789,7 +796,6 @@ void mv88e6xxx_get_regs(struct dsa_switch *ds, int port,
 	}
 }
 
-/* Must be called with SMI lock held */
 static int _mv88e6xxx_wait(struct dsa_switch *ds, int reg, int offset,
 			   u16 mask)
 {
@@ -839,14 +845,12 @@ int mv88e6xxx_eeprom_busy_wait(struct dsa_switch *ds)
 			      GLOBAL2_EEPROM_OP_BUSY);
 }
 
-/* Must be called with SMI lock held */
 static int _mv88e6xxx_atu_wait(struct dsa_switch *ds)
 {
 	return _mv88e6xxx_wait(ds, REG_GLOBAL, GLOBAL_ATU_OP,
 			       GLOBAL_ATU_OP_BUSY);
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_phy_read_indirect(struct dsa_switch *ds, int addr,
 					int regnum)
 {
@@ -865,7 +869,6 @@ static int _mv88e6xxx_phy_read_indirect(struct dsa_switch *ds, int addr,
 	return _mv88e6xxx_reg_read(ds, REG_GLOBAL2, GLOBAL2_SMI_DATA);
 }
 
-/* Must be called with SMI mutex held */
 static int _mv88e6xxx_phy_write_indirect(struct dsa_switch *ds, int addr,
 					 int regnum, u16 val)
 {