[PATCH v3 3/9] media: i2c: ds90ub960: Protect alias_use_mask with a mutex

Romain Gantois
2024-11-25T08:45:35Z

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@bootlin.com>
---
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