[i2c] Documentation issue on attaching new style drivers

[Ben Dooks]

Quoting from Documentation/i2c/writing-clients, the section
entitled "Standard Driver Model Binding ("New Style")" has
the following paragraph:

Drivers match devices when i2c_client.driver_name and the driver name are
the same; this approach is used in several other busses that don't have
device typing support in the hardware.  The driver and module name should
match, so hotplug/coldplug mechanisms will modprobe the driver.

Having tried this whilst upgrading an old driver in my own
tree, I found that this does not work, and that you need to
supply your own idtable for the .id_table entry.

I had a quick look in drivers/i2c/i2c-core.c and it seems
that the only thing the .match entry i2c_device_match() 
is doing is checking the driver's id_table, as so:

static int i2c_device_match(struct device *dev, struct device_driver *drv)
{
	struct i2c_client	*client = to_i2c_client(dev);
	struct i2c_driver	*driver = to_i2c_driver(drv);

	/* make legacy i2c drivers bypass driver model probing entirely;
	 * such drivers scan each i2c adapter/bus themselves.
	 */
	if (!is_newstyle_driver(driver))
		return 0;

	/* match on an id table if there is one */
	if (driver->id_table)
		return i2c_match_id(driver->id_table, client) != NULL;

	return 0;
}

Is the documentation wrong, and all drivers need to have an id_table
in them, or is the i2c-core.c wrong for only checking the id_table
entries?

My suspicion is that everyone is using the id_table as this can be
passed to the MODULE_DEVICE_TABLE() to allow autoloading of the
relevant modules? Note, the i2c_probe function will correctly pass
a NULL ID if there is no id_table present.

-- 
Ben (ben at fluff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'