Re: [RFC PATCH 7/7] i2c: core: hand over reserved devices when requesting ancillary addresses

Luca Ceresoli
2020-02-28T12:12:00Z

Hi,

On 21/02/20 11:13, Geert Uytterhoeven wrote:
> Hi Wolfram,
>
> On Thu, Feb 20, 2020 at 6:26 PM Wolfram Sang
> <wsa+renesas@sang-engineering.com> wrote:
>> 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!
>
>> --- 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).
>
>> +
>> + 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