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

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Date:   Mon, 24 May 2021 15:39:20 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.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

24.05.2021 11:54, Geert Uytterhoeven пишет:
> Hi Dmitry,
> 
> 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.
3. Disable compile-testing for HAVE_LEGACY_CLK

The third option is the simplest. If anyone will care to fix those
legacy platforms properly, then compile-testing could be re-enabled for
them. This is my proposal.