linux-kernel - Re: [PATCH V3 02/10] init.h: Fix the __setup

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Date:   Wed, 1 Jul 2020 10:37:59 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Anson Huang <anson.huang@....com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        "oleksandr.suvorov@...adex.com" <oleksandr.suvorov@...adex.com>,
        Stefan Agner <stefan.agner@...adex.com>,
        Peng Fan <peng.fan@....com>, Abel Vesa <abel.vesa@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        Andy Duan <fugang.duan@....com>,
        Daniel Baluta <daniel.baluta@....com>,
        YueHaibing <yuehaibing@...wei.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH V3 02/10] init.h: Fix the __setup_param() macro for module build

On Wed, Jul 1, 2020 at 7:14 AM Anson Huang <anson.huang@....com> wrote:
> > Subject: Re: [PATCH V3 02/10] init.h: Fix the __setup_param() macro for module build
> > On Mon, Jun 29, 2020 at 1:40 PM Anson Huang <anson.huang@....com>
> > wrote:
> > > It makes sense to drop the __setup() and __serup_param() in the #else
> > > block, just use one definition for all cases, if no one objects, I will remove
> > them in next patch series.
> >
> > Ok, sounds good. Note that there may be users of the plain __setup() that just
> > get turned into nops right now. Usually those are already enclosed in "#ifndef
> > MODULE", but if they are not, then removing the definition would cause a
> > build error.
> >
> > Have a look if you can find such instances, and either change the patch to add
> > the missing "#ifndef MODULE" checks, or just drop the __setup_param() and
> > leave the __setup() if it gets too complicated.
>
> Looks like the __setup_param() defined in "#ifndef MODULE" can NOT be used for
> MODULE build at all, so sharing same implementation is NOT available, so if it is NOT
> that critical, I plan to keep the #else block in this patch, let me know if you have further
> concern or any other suggestion, below is the build error reported for module build using
> __setup_param() implementation for built in.

I don't understand what your plan is here. Do you mean you will leave that
part of the clk driver as built-in?

> In file included from ./arch/arm64/include/asm/alternative.h:12,
>                  from ./arch/arm64/include/asm/lse.h:15,
>                  from ./arch/arm64/include/asm/cmpxchg.h:14,
>                  from ./arch/arm64/include/asm/atomic.h:16,
>                  from ./include/linux/atomic.h:7,
>                  from ./include/asm-generic/bitops/atomic.h:5,
>                  from ./arch/arm64/include/asm/bitops.h:26,
>                  from ./include/linux/bitops.h:29,
>                  from ./include/linux/kernel.h:12,
>                  from ./include/linux/clk.h:13,
>                  from drivers/clk/imx/clk.c:2:
> ./include/linux/init.h:177:16: error: variable ‘__setup_imx_keep_uart_earlycon’ has initializer but incomplete type
>   177 |  static struct obs_kernel_param __setup_##unique_id  \
>       |                ^~~~~~~~~~~~~~~~
> drivers/clk/imx/clk.c:157:1: note: in expansion of macro ‘__setup_param’
>   157 | __setup_param("earlycon", imx_keep_uart_earlycon,
>       | ^~~~~~~~~~~~~
> ./include/linux/init.h:180:7: warning: excess elements in struct initializer
>   180 |   = { __setup_str_##unique_id, fn, early }
>       |       ^~~~~~~~~~~~
> drivers/clk/imx/clk.c:157:1: note: in expansion of macro ‘__setup_param’
>   157 | __setup_param("earlycon", imx_keep_uart_earlycon,
>       | ^~~~~~~~~~~~~
> ./include/linux/init.h:180:7: note: (near initialization for ‘__setup_imx_keep_uart_earlycon’)

This error just means you can't have a __setup_param() call in a
loadable module,
which we already knew. If you need to do something with the clocks early on,
that has to be in built-in code and cannot be in a module. If you
don't need that
code, then you should just remove it from both the modular version and the
built-in version.

What is the purpose of that __setup_param() argument parsing in the
clock driver?

       Arnd