[RFC PATCH v2 6/6] i2c: core: hand over reserved devices when requesting ancillary addresses

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

With i2c_new_ancillary_address, we can check if the intended driver is
requesting a reserved address. Update the function to do these checks.
If the check passes, the "reserved" device will become a regular "dummy"
device.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---
 drivers/i2c/i2c-core-base.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 84464e439df5..81fb320de28d 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -974,7 +974,9 @@ struct i2c_client *i2c_new_ancillary_device(struct i2c_client *client,
 						const char *name,
 						u16 default_addr)
 {
-	struct device_node *np = client->dev.of_node;
+	struct device_node *reserved_np, *np = client->dev.of_node;
+	struct device *reserved_dev, *adapter_dev = &client->adapter->dev;
+	struct i2c_client *reserved_client = NULL;
 	u32 addr = default_addr;
 	int i;
 
@@ -984,7 +986,25 @@ struct i2c_client *i2c_new_ancillary_device(struct i2c_client *client,
 			of_property_read_u32_index(np, "reg", i, &addr);
 	}
 
-	dev_dbg(&client->adapter->dev, "Address for %s : 0x%x\n", name, addr);
+	dev_info(adapter_dev, "Address for %s : 0x%x\n", name, addr);
+
+	/* No need to scan muxes, siblings must sit on the same adapter */
+	reserved_dev = device_find_child(adapter_dev, &addr, __i2c_check_addr_busy);
+	if (reserved_dev) {
+		reserved_np = reserved_dev->of_node;
+		reserved_client = i2c_verify_client(reserved_dev);
+		put_device(reserved_dev);
+	}
+
+	if (reserved_client) {
+		if (reserved_np != np ||
+		    strcmp(reserved_client->name, I2C_RESERVED_DRV_NAME) != 0)
+			return ERR_PTR(-EBUSY);
+
+		strlcpy(reserved_client->name, I2C_DUMMY_DRV_NAME, sizeof(client->name));
+		return reserved_client;
+	}
+
 	return i2c_new_dummy_device(client->adapter, addr);
 }
 EXPORT_SYMBOL_GPL(i2c_new_ancillary_device);
-- 
2.20.1