linux-kernel - Re: [PATCH v1] kbuild: Disable compile testing if HAVE_LEGACY

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Date:   Tue, 25 May 2021 14:19:01 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Arnd Bergmann <arnd@...db.de>,
        Paul Burton <paul.burton@...s.com>,
        John Crispin <john@...ozen.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:TI ETHERNET SWITCH DRIVER (CPSW)" 
        <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v1] kbuild: Disable compile testing if HAVE_LEGACY_CLK enabled

Hi Krzysztof,

On Tue, May 25, 2021 at 2:04 PM Krzysztof Kozlowski
<krzysztof.kozlowski@...onical.com> wrote:
> On 24/05/2021 08:39, Dmitry Osipenko wrote:
> > 24.05.2021 11:54, Geert Uytterhoeven пишет:
> >> On Mon, May 24, 2021 at 1:26 AM Dmitry Osipenko <digetx@...il.com> wrote:
> >>> There are couple older platforms that can't be compile-tested because they
> >>> partially implement CLK API. It causes build failure of kernel drivers due
> >>> to the missing symbols of the unimplemented part of CLK API.
> >>>
> >>> These platforms are: ARM EP93XX, ARM OMAP1, m68k ColdFire, MIPS AR7,
> >>>                      MIPS Ralink.
> >>>
> >>> Disable compile-testing for HAVE_LEGACY_CLK=y.
> >>>
> >>> Reported-by: kernel test robot <lkp@...el.com>
> >>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> >>
> >> Thanks for your patch!
> >>
> >>> --- a/init/Kconfig
> >>> +++ b/init/Kconfig
> >>> @@ -131,7 +131,7 @@ config INIT_ENV_ARG_LIMIT
> >>>
> >>>  config COMPILE_TEST
> >>>         bool "Compile also drivers which will not load"
> >>> -       depends on HAS_IOMEM
> >>> +       depends on HAS_IOMEM && !HAVE_LEGACY_CLK
> >>
> >> That sounds a bit drastic to me.  Usually we just try to implement the
> >> missing functionality, or provide stubs.
> >> Which functions are missing?
> >
> > Everything that belongs to CONFIG_COMMON_CLK needs stubs.
> >
> > That is everything under CONFIG_HAVE_CLK [1], excluding functions
> > belonging to clk-devres.o and clk-bulk.o [2]. The HAVE_LEGACY_CLK
> > selects HAVE_CLK, but the COMMON_CLK is under HAVE_CLK too.
> >
> > [1]
> > https://elixir.bootlin.com/linux/v5.13-rc3/source/include/linux/clk.h#L786
> > [2]
> > https://elixir.bootlin.com/linux/v5.13-rc3/source/drivers/clk/Makefile#L3
> >
> > This problem is repeated over and over again for the past years. Some
> > maintainers are adding "depends on COMMON_CLK" for COMPILE_TEST of each
> > driver, but this doesn't solve the root of the problem, and thus, it's
> > constantly reoccurring.
> >
> > Recently Krzysztof Kozlowski added couple more clk stubs for MIPS, but
> > still lots of stubs are missing. Some platforms don't have any stubs at
> > all and apparently nobody cares to fix them.
> >
> > There 3 possible solutions:
> >
> > 1. Factor out COMMON_CLK from HAVE_LEGACY_CLK, if this is possible
> > 2. Build stubs universally, maybe using weak functions.
>
> I vote for this one - global stubs.

Yep.

> Or for a new one:
> 4. Disable COMPILE_TEST for specific platforms (mentioned in commit
> msg). Eventually could be like:
> config RALINK
>         depends !COMPILE_TEST || (COMPILE_TEST && COMMON_CLK)

That's a neat idea!

Of course there's a fifth option:

5. Convert legacy platforms to COMMON_CLK.

Which is already happening for ARM EP93XX.

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