[PATCH 3/9] media: i2c: ds90ub960: Protect alias_use_mask with a mutex

[Romain Gantois <romain.gantois@xxxxxxxxxxx>]

The alias_use_mask bitmap represents the occupation of an RX port's
hardware alias table. This bitmap 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 alias_use_mask bitmap.
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 alias_use_mask bitmap and its
underlying hardware table.

Signed-off-by: Romain Gantois <romain.gantois@xxxxxxxxxxx>
---
 drivers/media/i2c/ds90ub960.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/media/i2c/ds90ub960.c b/drivers/media/i2c/ds90ub960.c
index f86028894c78187257efc8fd70812387000796f7..84aa976bed2d74f1d639684601f4c1c38d748188 100644
--- a/drivers/media/i2c/ds90ub960.c
+++ b/drivers/media/i2c/ds90ub960.c
@@ -468,6 +468,8 @@ struct ub960_rxport {
 		};
 	} eq;
 
+	/* lock for alias_use_mask and associated registers */
+	struct mutex alias_mask_lock;
 	DECLARE_BITMAP(alias_use_mask, UB960_MAX_PORT_ALIASES);
 };
 
@@ -1031,11 +1033,15 @@ static int ub960_atr_attach_client(struct i2c_atr *atr, u32 chan_id,
 	struct ub960_rxport *rxport = priv->rxports[chan_id];
 	struct device *dev = &priv->client->dev;
 	unsigned int reg_idx;
+	int ret = 0;
+
+	mutex_lock(&rxport->alias_mask_lock);
 
 	reg_idx = find_first_zero_bit(rxport->alias_use_mask, UB960_MAX_PORT_ALIASES);
 	if (reg_idx >= UB960_MAX_PORT_ALIASES) {
 		dev_err(dev, "rx%u: alias pool exhausted\n", rxport->nport);
-		return -EADDRNOTAVAIL;
+		ret = -EADDRNOTAVAIL;
+		goto out_unlock;
 	}
 
 	set_bit(reg_idx, rxport->alias_use_mask);
@@ -1048,7 +1054,9 @@ static int ub960_atr_attach_client(struct i2c_atr *atr, u32 chan_id,
 	dev_dbg(dev, "rx%u: client 0x%02x assigned alias 0x%02x at slot %u\n",
 		rxport->nport, client->addr, alias, reg_idx);
 
-	return 0;
+out_unlock:
+	mutex_unlock(&rxport->alias_mask_lock);
+	return ret;
 }
 
 static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
@@ -1059,12 +1067,14 @@ static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
 	struct device *dev = &priv->client->dev;
 	unsigned int reg_idx;
 
+	mutex_lock(&rxport->alias_mask_lock);
+
 	reg_idx = find_first_zero_bit(rxport->alias_use_mask, UB960_MAX_PORT_ALIASES);
 
 	if (reg_idx >= UB960_MAX_PORT_ALIASES) {
 		dev_err(dev, "rx%u: client 0x%02x is not mapped!\n",
 			rxport->nport, client->addr);
-		return;
+		goto out_unlock;
 	}
 
 	clear_bit(reg_idx, rxport->alias_use_mask);
@@ -1073,6 +1083,9 @@ static void ub960_atr_detach_client(struct i2c_atr *atr, u32 chan_id,
 
 	dev_dbg(dev, "rx%u: client 0x%02x released at slot %u\n", rxport->nport,
 		client->addr, reg_idx);
+
+out_unlock:
+	mutex_unlock(&rxport->alias_mask_lock);
 }
 
 static const struct i2c_atr_ops ub960_atr_ops = {
@@ -3177,6 +3190,8 @@ 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->alias_mask_lock);
+
 		kfree(rxport);
 		priv->rxports[nport] = NULL;
 	}
@@ -3398,6 +3413,7 @@ static int ub960_parse_dt_rxport(struct ub960_data *priv, unsigned int nport,
 		goto err_put_remote_fwnode;
 
 	bitmap_zero(rxport->alias_use_mask, UB960_MAX_PORT_ALIASES);
+	mutex_init(&rxport->alias_mask_lock);
 
 	return 0;
 

-- 
2.47.0