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

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Message-ID: <56FCC70D.30306@uclinux.org>
Date:	Thu, 31 Mar 2016 16:43:25 +1000
From:	Greg Ungerer <gerg@...inux.org>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	linux-m68k <linux-m68k@...ts.linux-m68k.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH] gpio: add a userspace chardev ABI for GPIOs

Hi Alexandre,

On 31/03/16 15:59, Alexandre Courbot wrote:
> On Wed, Mar 30, 2016 at 10:49 AM, Greg Ungerer <gerg@...inux.org> 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.

Thanks for letting me know. I wasn't going to rush any fixes,
happy to let Linus decide how to handle it.

Regards
Greg