linux-kernel - Re: [PATCH 15/15] OF: remove #ifdef from linux/of

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Message-ID: <CAL_JsqLRJ1cEWBfAdHEyngJHQKauJ6XzWH2JwXh1qDusMkzUGA@mail.gmail.com>
Date:	Tue, 4 Jun 2013 17:24:51 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	patches@...ts.linaro.org, Rob Herring <rob.herring@...xeda.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 15/15] OF: remove #ifdef from linux/of_platform.h

On Tue, Jun 4, 2013 at 12:51 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Tuesday 04 June 2013, Rob Herring wrote:
>> On Sat, Jun 1, 2013 at 3:57 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> > On Saturday 01 June 2013, Rob Herring wrote:
>> >> No, we still need empty functions. Here is what of_device.h looks like:
>> >>
>> >> http://tinyurl.com/l2azz5m
>> >>
>> >> BTW, it has your ack.
>> >>
>> >
>> > Could you add a patch on top that only puts the function declarations
>> > inside of #ifdef that don't have an inline wrapper?
>>
>> I'm confused. You mean that DO have an inline? Like this:
>>
>> void foo(void);
>>
>> #ifdef CONFIG_OF
>> void bar(void);
>> #else
>> static inline void bar(void) {}
>> #endif
>
> Yes, sorry. That's what I meant.
>
>> > It's really annoying to have to change the header file every time one
>> > needs to call a function from a driver in the DT-only case.
>>
>> The functions without inlines are ones that drivers should not call
>> and should only be called from OF enabled code. That's why we have not
>> done a complete pass of adding inlines for everything.
>
> The problem is that it's a bad default. The convention in kernel code
> is not to hide declarations in #ifdef, for multiple reasons:
>
> * It avoids unnecessary code rebuilds when the symbol changes between
>   two 'make' runs.
>
> * It lets drivers and platform code call the function from dead code
>   without causing a build error, thus improving compile coverage.
>
> * It's much nicer to read when can write your code like
>
> void __init exynos_init_io(struct map_desc *mach_desc, int size)
> {
>         if (IS_ENABLED_(CONFIG_OF) && initial_boot_params)
>                 of_scan_flat_dt(exynos_fdt_map_chipid, NULL);
>         else
>                 iotable_init(exynos_iodesc, ARRAY_SIZE(exynos_iodesc));
>         ...
> }
>
> instead of
>
> void __init exynos_init_io(struct map_desc *mach_desc, int size)
> {
> #ifdef CONFIG_OF
>         if (initial_boot_params)
>                 of_scan_flat_dt(exynos_fdt_map_chipid, NULL);
>         else
> #endif
>                 iotable_init(exynos_iodesc, ARRAY_SIZE(exynos_iodesc));
>         ...
> }
>
> The first one looks like actual C code, the second is really ugly,
> and an inline wrapper wouldn't even do the right thing here.

Right. I get all that. You still have to go add inlines if you want to make:

if (IS_ENABLED(CONFIG_OF))
    of_foo();

just be:

of_foo();

There are situations for both and only inlines cover both cases. I
don't see a reason we would want to allow the first case and not allow
the second case. I am tired of taking patches adding the inlines 1 by
1, so perhaps we need to refactor the OF headers to better separate
core infrastructure includes vs. driver only includes if that is
really a concern.

Rob
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