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

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Message-ID: <CAMuHMdW+e8qvKsf4Ub1zNnBgBX6TKGmUKHSDK0jy05H5gmrh+g@mail.gmail.com>
Date:   Mon, 31 May 2021 09:32:04 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Randy Dunlap <rdunlap@...radead.org>,
        David Daney <david.daney@...ium.com>
Cc:     kernel test robot <lkp@...el.com>, Andrew Lunn <andrew@...n.ch>,
        kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rich Felker <dalias@...c.org>
Subject: Re: ERROR: modpost: "__delay" [drivers/net/mdio/mdio-cavium.ko] undefined!

CC David (original author, asked by driver location change)

On Mon, May 31, 2021 at 9:29 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> On Mon, May 31, 2021 at 2:05 AM Randy Dunlap <rdunlap@...radead.org> wrote:
> > On 5/29/21 4:25 PM, kernel test robot wrote:
> > > 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.
>
> Hence it must not be used by drivers, as it might give the false assumption
> of working everywhere.  While drivers/net/mdio/mdio-cavium is
> platform-specific, code might be copied in a new driver, less restricted
> to a specific platform.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds