linux-kernel - Re: drivers/ata/ahci_st.c:229:34: warning: unused variable 'st_ahci

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Message-ID: <4517c95f-1dad-5a8c-5202-073d0a7eff29@opensource.wdc.com>
Date:   Thu, 13 Oct 2022 15:13:33 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org
Cc:     llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: Re: drivers/ata/ahci_st.c:229:34: warning: unused variable
 'st_ahci_match'

On 10/12/22 15:37, kernel test robot wrote:
> Hi Damien,
> 
> First bad commit (maybe != root cause):
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   49da070062390094112b423ba443ea193527b2e4
> commit: ecf8322f464d62759d838ea62cdeff6966a60134 ata: ahci_st: Enable compile test
> date:   3 weeks ago
> config: mips-randconfig-r023-20221012
> compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 791a7ae1ba3efd6bca96338e10ffde557ba83920)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install mips cross compiling tool for clang build
>         # apt-get install binutils-mipsel-linux-gnu
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ecf8322f464d62759d838ea62cdeff6966a60134
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout ecf8322f464d62759d838ea62cdeff6966a60134
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash drivers/ata/
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):
> 
>>> drivers/ata/ahci_st.c:229:34: warning: unused variable 'st_ahci_match' [-Wunused-const-variable]
>    static const struct of_device_id st_ahci_match[] = {
>                                     ^
>    1 warning generated.
> 
> 
> vim +/st_ahci_match +229 drivers/ata/ahci_st.c
> 
> 76884cb2f7da52 Lee Jones          2014-02-26  228  
> 09de99db23df55 Kiran Padwal       2014-07-22 @229  static const struct of_device_id st_ahci_match[] = {
> 76884cb2f7da52 Lee Jones          2014-02-26  230  	{ .compatible = "st,ahci", },
> 5e776d7b20f040 Geert Uytterhoeven 2022-03-03  231  	{ /* sentinel */ }
> 76884cb2f7da52 Lee Jones          2014-02-26  232  };
> 76884cb2f7da52 Lee Jones          2014-02-26  233  MODULE_DEVICE_TABLE(of, st_ahci_match);
> 76884cb2f7da52 Lee Jones          2014-02-26  234  
> 
> :::::: The code at line 229 was first introduced by commit
> :::::: 09de99db23df55c7415d110f6c62281dedd77384 ahci: st: Make of_device_id array const
> 
> :::::: TO: Kiran Padwal <kiran.padwal21@...il.com>
> :::::: CC: Tejun Heo <tj@...nel.org>

I am at a loss with this one... There are plenty of patterns similar to
drivers/ata/ahci_st.c doing something like:

static const struct of_device_id st_ahci_match[] = {

        { .compatible = "st,ahci", },

        { /* sentinel */ }

};

MODULE_DEVICE_TABLE(of, st_ahci_match);

For instance, in drivers/pwm/pwm-sti.c, we have:

static const struct of_device_id sti_pwm_of_match[] = {

        { .compatible = "st,sti-pwm", },

        { /* sentinel */ }

};

MODULE_DEVICE_TABLE(of, sti_pwm_of_match);

And countless others like this for STI and other arch too.

So if CONFIG_MODULE is not enabled, how come we are not submerged with
warnings about unused variables ? Is mips arch special in this regard ?
Or am I missing something ?

-- 
Damien Le Moal
Western Digital Research