linux-kernel - Re: [PATCH] gpio: Do not accept gpio chip additions before gpiolib initialization

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Date:	Thu, 31 Mar 2016 14:57:39 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: Do not accept gpio chip additions before gpiolib initialization

On Wed, Mar 30, 2016 at 6:16 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 03/30/2016 01:37 AM, Alexandre Courbot wrote:
>>
>> On Wed, Mar 30, 2016 at 3:20 AM, Guenter Roeck <linux@...ck-us.net> wrote:
>>>
>>> Since commit ff2b13592299 ("gpio: make the gpiochip a real device"),
>>> attempts to add a gpio chip prior to gpiolib initialization cause the
>>> system to crash. Dump a warning to the console and return an error
>>> if the situation is encountered.
>>
>>
>> Mmm I see the problem but this could seriously delay the availability
>> of some GPIOs that are useful for early system boot.
>>
>> I have not followed the GPIO device patches as closely as I should
>> have, but shouldn't you be able to register a GPIO chip without
>> immediately presenting it to user-space, for internal kernel needs? If
>> gpiolib is not initialized, then device-related operations would be
>> skipped, and gpiolib_dev_init() could then parse the list of
>> registered chips and fix them up when it gets called.
>>
>> Again, I'm speaking without real knowledge here, but that pattern
>> seems more resilent to me.
>>
> You are absolutely right, but my knowledge of gpiolib is not good enough
> to make that change. See this as a band-gap; it is better than just
> crashing.

Actually, the following may be simpler:

Why not add a check in gpiochip_add_data() that will directly call
gpiolib_dev_init() if required? Then gpiolib_dev_init() could also
check whether it has already been called in that context and become a
no-op for when it is later called from core_initcall. Is there
anything that would prevents this from being a viable fix?