media: i2c: ds90ub960: Protect alias_use_mask with a mutex

The aliased_addrs list represents the occupation of an RX port's hardware
alias table. This list and the underlying hardware table are only accessed
in the attach/detach_client() callbacks.

These functions are only called from a bus notifier handler in i2c-atr.c,
which is always called with the notifier chain's semaphore held. This
indirectly prevents concurrent access to the aliased_addrs list.
However, more explicit and direct locking is preferable. Moreover, with the
introduction of dynamic address translation in a future patch, the
attach/detach_client() callbacks will be called from outside of the
notifier chain's read section.

Introduce a mutex to protect access to the aliased_addrs list and its
underlying hardware table.

Tested-by: Tomi Valkeinen <[email protected]>
Signed-off-by: Romain Gantois <[email protected]>
Acked-by: Andi Shyti <[email protected]>
Signed-off-by: Wolfram Sang <[email protected]>

Author: rgantois

drivers/media/i2c/ds90ub960.c

@@ -27,6 +27,7 @@
  */
 
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/fwnode.h>
@@ -478,6 +479,8 @@ struct ub960_rxport {
 		};
 	} eq;
 
+	/* lock for aliased_addrs and associated registers */
+	struct mutex aliased_addrs_lock;
 	u16 aliased_addrs[UB960_MAX_PORT_ALIASES];
 };
 
@@ -1054,6 +1057,8 @@ static int ub960_atr_attach_client(struct i2c_atr *atr, u32 chan_id,
 	struct device *dev = &priv->client->dev;
 	unsigned int reg_idx;
 
+	guard(mutex)(&rxport->aliased_addrs_lock);
+
 	for (reg_idx = 0; reg_idx < ARRAY_SIZE(rxport->aliased_addrs); reg_idx++) {
 		if (!rxport->aliased_addrs[reg_idx])
 			break;
@@ -1085,6 +1090,8 @@ static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
 	struct device *dev = &priv->client->dev;
 	unsigned int reg_idx;
 
+	guard(mutex)(&rxport->aliased_addrs_lock);
+
 	for (reg_idx = 0; reg_idx < ARRAY_SIZE(rxport->aliased_addrs); reg_idx++) {
 		if (rxport->aliased_addrs[reg_idx] == client->addr)
 			break;
@@ -3235,6 +3242,8 @@ static void ub960_rxport_free_ports(struct ub960_data *priv)
 		fwnode_handle_put(rxport->source.ep_fwnode);
 		fwnode_handle_put(rxport->ser.fwnode);
 
+		mutex_destroy(&rxport->aliased_addrs_lock);
+
 		kfree(rxport);
 		priv->rxports[nport] = NULL;
 	}
@@ -3455,6 +3464,8 @@ static int ub960_parse_dt_rxport(struct ub960_data *priv, unsigned int nport,
 	if (ret)
 		goto err_put_remote_fwnode;
 
+	mutex_init(&rxport->aliased_addrs_lock);
+
 	return 0;
 
 err_put_remote_fwnode: