Re: [PATCH] gpio: add a userspace chardev ABI for GPIOs

[Alexandre Courbot <gnurou@xxxxxxxxx>]

On Wed, Mar 30, 2016 at 10:49 AM, Greg Ungerer <gerg@xxxxxxxxxxx> wrote:
> Hi Linus,
>
> Commit 3c702e99 ("gpio: add a userspace chardev ABI for GPIOs")
> breaks booting on all my m68k/ColdFire platforms (with MMU and
> without). They all hang during the boot up, the last console
> trace is:
>
>   ...
>   NR_IRQS:256
>    clocksource: pit: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1467848399018 ns
>    Calibrating delay loop... 1042.02 BogoMIPS (lpj=5210112)
>    pid_max: default: 32768 minimum: 301
>    Mount-cache hash table entries: 2048 (order: 0, 8192 bytes)
>    Mountpoint-cache hash table entries: 2048 (order: 0, 8192 bytes)
>
> I traced this back to gpiochip_add_data() when it does the
> device_add() call. On my platforms this is being called
> before gpiolib_dev_init(), and this seems to be the issue.
> So gpio_bus_type has not been registered as a bus yet.
>
> The lowest level ColdFire gpio code (arch/m68k/coldfire/gpio.c)
> calls its setup from core_initcall() - and this will call
> gpiochip_add_data(). This is being called first, before
> the core_initcall() for gpiolib_dev_init().

We got a similar report with an alternative workaround:

https://lkml.org/lkml/2016/3/29/714

> I can fix by changing the core_initcall() in coldfire/gpio.c
> to something like postcore_initcall() and that fixes the boot
> problem.
>
> What do you think?
> Would you expect that all callers of gpiochip_add_data()
> should be after core_initcall()?

As you can see on the discussion thread above, there are several
candidate fixes - I have been away from GPIO for too long to make a
good decision, but I'm sure Linus can make the call.
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