From mboxrd@z Thu Jan  1 00:00:00 1970
From: 21cnbao@gmail.com (Barry Song)
Date: Thu, 19 May 2011 20:35:59 +0800
Subject: [PATCH 02/10] mach-u300: rewrite gpio driver, move to drivers/gpio
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References: <1303910002-3333-1-git-send-email-linus.walleij@stericsson.com>
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To: linux-arm-kernel@lists.infradead.org
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2011/5/19 Linus Walleij <linus.walleij@linaro.org>:
> On Thu, May 19, 2011 at 1:38 PM, Barry Song <21cnbao@gmail.com> wrote:
>
>>> -arch_initcall(u300_gpio_init);
>>> -module_exit(u300_gpio_exit);
>>>
>> looks like the driver can't be a real module, is the module_exit
>> suitable? it looks strange module_exit plays together with
>> arch_initcall.
>
> It's a rather common design pattern in the kernel for early
> platform drivers. Either the dependencies are resolved by the
> different initlevels or they are resolved in probe order with
> loadable modules. Module load will call all initlevels in order.
>
> It is not elegant but it is common.

Linus, thanks for your reply. module_exit and related functions are
really useless codes. but people have done that before, then we have
no way except following.
u300_gpio_exit never gets chance to run and when we disassemble
vmlinux, u300_gpio_exit()  function should be not in the final binary
at all, just a symbol name is left.

>
>> guess symbol u300_gpio_exit will finally lose in the last vmlinux
>> since it is in exit section and built-in kernel.
>
> Yes. And if you one day, to do some testing, compile and load it
> as module and unload it, it is handy.
>
> I have other drivers where I simply don't have an exit function
> but this one I have actually used.
>
>> another problem i see is after moving gpio/pinmux to drivers as
>> platform device, codes in arch/arm/plat(mach) can't ?call gpio/pinmux
>> api before the related platform devices registerred. that will
>> required these platform devices enter system earlier.
>
> This is exactly the reason why the u300 gpio driver needs to
> be initialized in an arch_initcall().
>
> Yours,
> Linus Walleij
>