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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Mon, 21 Nov 2022 08:45:14 +0900
Message-ID: <CAK7LNASxxzA1OEGuJR=BU=6G8XaatGx+gDCMe2s9Y3MRcwptYw@mail.gmail.com>
Subject: Re: [PATCH 11/18] platform/x86: int3472: fix object shared between
 several modules
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexander Lobakin <alobakin@pm.me>,
        linux-kbuild@vger.kernel.org, Nicolas Schier <nicolas@fjasle.eu>,
        Jens Axboe <axboe@kernel.dk>,
        Boris Brezillon <bbrezillon@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Tony Luck <tony.luck@intel.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Derek Chickles <dchickles@marvell.com>,
        Ioana Ciornei <ioana.ciornei@nxp.com>,
        Salil Mehta <salil.mehta@huawei.com>,
        Sunil Goutham <sgoutham@marvell.com>,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        Daniel Scally <djrscally@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        NXP Linux Team <linux-imx@nxp.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Precedence: bulk

On Mon, Nov 21, 2022 at 5:55 AM Hans de Goede <hdegoede@redhat.com> wrote:
>
> Hi,
>
> On 11/20/22 14:55, Andy Shevchenko wrote:
> > On Sat, Nov 19, 2022 at 11:08:17PM +0000, Alexander Lobakin wrote:
> >> common.o is linked to both intel_skl_int3472_{discrete,tps68470}:
> >>
> >>> scripts/Makefile.build:252: ./drivers/platform/x86/intel/int3472/Makefile:
> >>> common.o is added to multiple modules: intel_skl_int3472_discrete
> >>> intel_skl_int3472_tps68470
> >>
> >> Although both drivers share one Kconfig option
> >> (CONFIG_INTEL_SKL_INT3472), it's better to not link one object file
> >> into several modules (and/or vmlinux).
> >> Under certain circumstances, such can lead to the situation fixed by
> >> commit 637a642f5ca5 ("zstd: Fixing mixed module-builtin objects").
> >>
> >> Introduce the new module, intel_skl_int3472_common, to provide the
> >> functions from common.o to both discrete and tps68470 drivers. This
> >> adds only 3 exports and doesn't provide any changes to the actual
> >> code.
>
> Replying to Andy's reply here since I never saw the original submission
> which was not Cc-ed to platform-driver-x86@vger.kernel.org .
>
> As you mention already in the commit msg, the issue from:
>
> commit 637a642f5ca5 ("zstd: Fixing mixed module-builtin objects")
>
> is not an issue here since both modules sharing the .o file are
> behind the same Kconfig option.
>
> So there is not really an issue here and common.o is tiny, so
> small chances are it does not ever increase the .ko size
> when looking a the .ko size rounded up to a multiple of
> the filesystem size.
>
> At the same time adding an extra module does come with significant
> costs, it will eat up at least 1 possibly more then 1 fs blocks
> (I don't know what the module header size overhead is).
>
> And it needs to be loaded separately and module loading is slow;
> and it will grow the /lib/modules/<kver>/modules.* sizes.
>
> So nack from me for this patch, since I really don't see
> it adding any value.


This does have a value.

This clarifies the ownership of the common.o,
in other words, makes KBUILD_MODNAME deterministic.


If an object belongs to a module,
KBUILD_MODNAME is defined as the module name.

If an object is always built-in,
KBUILD_MODNAME is defined as the basename of the object.


Here is a question:
if common.o is shared by two modules intel_skl_int3472_discrete
and intel_skl_int3472_tps68470, what should KBUILD_MODNAME be?


I see some patch submissions relying on the assumption that
KBUILD_MODNAME is unique.
We cannot determine KBUILD_MODNAME correctly if an object is shared
by multiple modules.


BTW, this patch is not the way I suggested.
The Suggested-by should not have been there
(or at least Reported-by)


You argued "common.o is tiny", so I would vote for
making them inline functions, like


https://lore.kernel.org/linux-kbuild/20221119225650.1044591-2-alobakin@pm.me/T/#u


> Regards,
>
> Hans
>
>
>
>
>
> >
> > ...
> >
> >> +MODULE_IMPORT_NS(INTEL_SKL_INT3472);
> >> +
> >
> > Redundant blank line. You may put it to be last MODULE_*() in the file, if you
> > think it would be more visible.
> >
> >>  MODULE_DESCRIPTION("Intel SkyLake INT3472 ACPI Discrete Device Driver");
> >>  MODULE_AUTHOR("Daniel Scally <djrscally@gmail.com>");
> >>  MODULE_LICENSE("GPL v2");
> >
> > ...
> >
> >> +MODULE_IMPORT_NS(INTEL_SKL_INT3472);
> >> +
> >>  MODULE_DESCRIPTION("Intel SkyLake INT3472 ACPI TPS68470 Device Driver");
> >>  MODULE_AUTHOR("Daniel Scally <djrscally@gmail.com>");
> >>  MODULE_LICENSE("GPL v2");
> >
> > Ditto. And the same to all your patches.
> >
>


-- 
Best Regards
Masahiro Yamada