Re: [PATCH] Input: tca6416-keypad: Change to module_init()

[Magnus Damm <magnus.damm@gmail.com>]

On Tue, Mar 22, 2011 at 11:28 PM, Mark Brown
<broonie@opensource.wolfsonmicro.com> wrote:
> On Tue, Mar 22, 2011 at 11:26:19PM +0900, Magnus Damm wrote:
>
>> The tca6416 driver makes use of the I2C bus for chatting
>> with the actual hardware device. Without this patch both
>> the I2C bus driver and the tca6416 driver are initialized
>> at the subsys_initcall() level. This may lead to problems
>> with the tca6416 driver being initialized before the I2C
>> bus driver.
>
> While this change seems reasonable I'm curious what the problems caused
> by out of order registration are?

The boot up time is delayed with 5 seconds or so due to a delay that
only happens if subsys_initcall() level is used for both tca6416 and
the I2C driver. By disabling the tca6416 driver in the kernel
configuration the delay goes away. I have not tracked it down further
than using module_init() instead of subsys_initcall() in the tca6416
driver. This because tca6416-keypad.c is the only keyboard driver that
uses subsys_initcall().

If I enable initcall_debug then I get this output:

calling  input_init+0x0/0x114 @ 1
initcall input_init+0x0/0x114 returned 0 after 0 usecs
calling  tca6416_keypad_init+0x0/0x10 @ 1
initcall tca6416_keypad_init+0x0/0x10 returned 0 after 0 usecs
calling  sh_mobile_i2c_adap_init+0x0/0xc @ 1
i2c-sh_mobile i2c-sh_mobile.0: clocks managed by runtime pm
input: tca6408-keys as
/devices/platform/i2c-sh_mobile.0/i2c-0/0-0020/input/input0
[delay]

If my interpretation of the log above is correct then
tca6416_keypad_init() is executed before sh_mobile_i2c_adap_init().

As for link order, i2c is located after input in driver/Makefile. I
believe that matches well with the log above.

Thanks,

/ magnus