Hi,

On 21/02/20 11:13, Geert Uytterhoeven wrote:

Hi Wolfram,

On Thu, Feb 20, 2020 at 6:26 PM Wolfram Sang
[off-list ref] wrote:

quoted

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>

Thanks for your patch!

quoted

--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c

@@ -975,6 +975,8 @@ struct i2c_client *i2c_new_ancillary_device(struct i2c_client *client,
                                                u16 default_addr)
 {
        struct device_node *np = client->dev.of_node;
+       struct device *reserved_dev, *adapter_dev = &client->adapter->dev;
+       struct i2c_client *reserved_client;
        u32 addr = default_addr;
        int i;

@@ -984,7 +986,21 @@ 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);
+       reserved_client = i2c_verify_client(reserved_dev);
+
+       if (reserved_client) {
+               if (reserved_client->dev.of_node != np ||
+                   strcmp(reserved_client->name, I2C_RESERVED_DRV_NAME) != 0)
+                       return ERR_PTR(-EBUSY);

Missing put_device(reserved_dev).

quoted

+
+               strlcpy(reserved_client->name, I2C_DUMMY_DRV_NAME, sizeof(client->name));

Any strong reason for not giving the device a more informative name?
Reading "dummy" in several /sys/bus/i2c/devices/?-????/name files is not
helping. Using the 'name' string that is passed to
i2c_new_ancillary_device() would be way better, perhaps prefixed by
dev->name. But this opens the question of why not doing it in
i2c_new_dummy_device() as well, which currently receives no "name"
parameter.

Of course this is not strictly related to this patch and can be done in
a later step.

About the patch itself, except for the issues pointed out by Geert the
approach looks generally good to me.

-- 
Luca