On Wed, Mar 23, 2011 at 1:31 AM, Mark Brown
[off-list ref] wrote:

On Wed, Mar 23, 2011 at 01:20:23AM +0900, Magnus Damm wrote:

quoted

On Wed, Mar 23, 2011 at 12:57 AM, Paul Mundt [off-list ref] wrote:

quoted

quoted

In this case I would suspect general indifference or simply copying other
drivers. I2C is a bit of a tricky case with regards to ordering in
general, but at least input devices are relatively straightforward.

quoted

I remember having to move the init order around at least once before
in the case of i2c, so I'm not so surprised when new initcall issues
come up now and then.

It's mostly an issue for PMICs (and possibly some other similar things)
so that the regulators are present before their consumers try to start.
I'm not aware of any issues with I2C itself.

I recall changing my i2c bus driver i2c-sh_mobile.c from module_init()
to subsys_initcall() a few years ago (see
ccb3bc16b4891a82649d4bccbeefe60b1d9a62e2) - this because regular
drivers tend to use module_init() and following the link order is not
enough. I think the patch for tca6416 is more or less the same issue
but on subsys_initcall() level instead.

I'm not sure if this is i2c specific though - in general you probably
need to register the parent bus driver first.

I've seen some SH-Mobile designs with PMICs, and they all use a
dedicated i2c bus.

quoted

The "may" above comes from that I don't know the i2c bus driver
initcall time on non-SH-Mobile platforms. So this may trigger on other
platforms, or it may not depending on their cpu/board code and I2c bus
driver.

In general embedded platforms register I2C early as things like PMICs
typically hang off them.  Grant was trying to push people to use
deferred registration for this stuff but it didn't happen yet and I'd
personally be more comfortable with more infastructure supporting that.

The dependency tracking is a bit primitive with only initcalls. I
wouldn't mind something like this:

-static int __init tca6416_keypad_init(void)
-{
-	return i2c_add_driver(&tca6416_keypad_driver);
-}
-
-subsys_initcall(tca6416_keypad_init);
-
-static void __exit tca6416_keypad_exit(void)
-{
-	i2c_del_driver(&tca6416_keypad_driver);
-}
-module_exit(tca6416_keypad_exit);
+i2c_driver_module(&tca6416_keypad_driver);

Cheers,

/ magnus