linux-kernel - Re: ERROR: modpost: "__delay" [drivers/net/mdio/mdio-cavium.ko] undefined!

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Date:   Sun, 30 May 2021 17:05:42 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     kernel test robot <lkp@...el.com>, Andrew Lunn <andrew@...n.ch>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Rich Felker <dalias@...c.org>
Subject: Re: ERROR: modpost: "__delay" [drivers/net/mdio/mdio-cavium.ko]
 undefined!

On 5/29/21 4:25 PM, kernel test robot wrote:
> Hi Andrew,
> 
> First bad commit (maybe != root cause):
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   df8c66c4cfb91f2372d138b9b714f6df6f506966
> commit: a9770eac511ad82390b9f4a3c1728e078c387ac7 net: mdio: Move MDIO drivers into a new subdirectory
> date:   9 months ago
> config: sh-allmodconfig (attached as .config)
> compiler: sh4-linux-gcc (GCC) 9.3.0
> 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
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a9770eac511ad82390b9f4a3c1728e078c387ac7
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout a9770eac511ad82390b9f4a3c1728e078c387ac7
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=sh 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All errors (new ones prefixed by >>, old ones prefixed by <<):
> 
>>> ERROR: modpost: "__delay" [drivers/net/mdio/mdio-cavium.ko] undefined!

Just a comment here.  kernel test robot has reported this issue
5 times in 2021 that I know of -- and I could have missed some.

I see that Geert recently (June 2020) reverted the
EXPORT_SYMBOL(__delay) in arch/sh/lib/delay.c, with this comment:

    __delay() is an internal implementation detail on several architectures.
    Drivers should not call __delay() directly, as it has non-standardized
    semantics, or may not even exist.
    Hence there is no need to export __delay() to modules.

    See also include/asm-generic/delay.h:
    
        /* Undefined functions to get compile-time errors */
        ...
        extern void __delay(unsigned long loops);

However, s/several architectures/all but one architecture: SH/.
All architectures except for SH provide either an exported function,
an inline function, or a macro for __delay(). Yeah, they probably
don't all do the same delay.

-- 
~Randy