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

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Date:	Wed, 30 Mar 2016 02:16:02 -0700
From:	Guenter Roeck <linux@...ck-us.net>
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 Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: Do not accept gpio chip additions before gpiolib
 initialization

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.

Guenter