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

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Date:   Wed, 1 Jul 2020 09:27:07 +0000
From:   Anson Huang <anson.huang@....com>
To:     Arnd Bergmann <arnd@...db.de>
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

Hi, Arnd


> 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?

I meant I will leave the #else block of __setup_param() defined as nothing as below to
make module build passed.

#define __setup_param(str, unique_id, fn, early)        /* nothing */

> 
> > 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?
> 

We need the code for proper uart clock management of earlycon, from the code, it
is trying to keep console uart clock enabled during kernel boot up. 

Thanks,
Anson