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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 19 Apr 2021 16:15:36 +0200
Message-ID: <CAMuHMdX1D+2iLPEDzG9BiR8bu-dEBmE-=w0nFMhF8ojD7rCfzg@mail.gmail.com>
Subject: Re: [PATCH] i2c: I2C_HISI should depend on ARCH_HISI && ACPI
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Yicong Yang <yangyicong@hisilicon.com>,
        Wei Xu <xuwei5@hisilicon.com>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        Dmitry Osipenko <digetx@gmail.com>,
        Linux I2C <linux-i2c@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linuxarm <linuxarm@huawei.com>
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Precedence: bulk

Hi Andy,

On Mon, Apr 19, 2021 at 3:58 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Mon, Apr 19, 2021 at 4:54 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Mon, Apr 19, 2021 at 3:35 PM Andy Shevchenko
> > <andy.shevchenko@gmail.com> wrote:
> > > On Mon, Apr 19, 2021 at 4:02 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > On Thu, Apr 15, 2021 at 10:50 AM Andy Shevchenko
> > > > <andy.shevchenko@gmail.com> wrote:
> > > > > On Thu, Apr 15, 2021 at 3:43 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > > > On Wed, Apr 14, 2021 at 9:14 PM Andy Shevchenko
> > > > > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > > > > On Wed, Apr 14, 2021 at 08:55:21PM +0200, Geert Uytterhoeven wrote:
> > > > > > > > On Wed, Apr 14, 2021 at 8:18 PM Andy Shevchenko
> > > > > > > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > > > > > > On Wed, Apr 14, 2021 at 08:06:18PM +0200, Geert Uytterhoeven wrote:
> > > > > > > > > > On Wed, Apr 14, 2021 at 11:24 AM Yicong Yang <yangyicong@hisilicon.com> wrote:
> > >
> > > ...
> > >
> > > > > > > > > > I guess it's still fine to add a dependency on ACPI?
> > > > > > > > >
> > > > > > > > > But why?
> > > > > > > >
> > > > > > > > Please tell me how/when the driver is used when CONFIG_ACPI=n.
> > > > > > >
> > > > > > > I'm not using it at all. Ask the author :-)
> > > > > > >
> > > > > > > But if we follow your logic, then we need to mark all the _platform_ drivers
> > > > > > > for x86 world as ACPI dependent? This sounds ugly.
> > > > > >
> > > > > > Do all other x86 platform drivers have (1) an .acpi_match_table[] and
> > > > > > (2) no other way of instantiating their devices?
> > > > > > The first driver from the top of my memory I looked at is rtc-cmos:
> > > > > > it has no .acpi_match_table[], and the rtc-cmos device is instantiated
> > > > > > from arch/x86/kernel/rtc.c.
> > > > > >
> > > > > > For drivers with only an .of_match_table(), and no legacy users
> > > > > > instantiating platform devices, we do have dependencies on OF.
> > > > >
> > > > > This is not true. Entire IIO subsystem is an example.
> > > >
> > > > Do you care to elaborate?
> > > > Three quarters of the IIO drivers are I2C and SPI drivers, and thus not
> > > > subject to the above.
> > >
> > > It seems I missed that you are talking about platform device drivers.
> >
> > OK.
> >
> > > In any case it's not true. We have the platform drivers w/o legacy
> > > users that are not dependent on OF.
> >
> > Example? ;-)
>
> i2c-owl.c

I2C_OWL depends on ARCH_ACTIONS || COMPILE_TEST

(arm32) ARCH_ACTIONS depends on ARCH_MULTI_V7
                     depends on ARCH_MULTIPLATFORM
                     ARCH_MULTIPLATFORM selects USE_OF
                     USE_OF selects OF
ARCH_MULTI_V7 selects ARCH_MULTI_V6_V7

(arm64) ARM64 selects OF

so we do have a dependency on OF, unless we're compile-testing.

> > > They may _indirectly_ be dependent, but this is fine as I stated above
> > > when suggested to move ACPI dependency on ARCH_xxx level.
> >
> > As per the response from the driver maintainer
> > https://lore.kernel.org/linux-arm-kernel/bd8db435-24e1-5ab3-6b35-1d4d8a292a7e@hisilicon.com/,
> > there is no dependency on ARCH_HISI, so moving the ACPI dependency
> > up won't help.
>
> So, an ACPI dependency is simply not applicable here as it's a compile
> dependency as well, which is not a limitation for this driver. Again,
> talk to Masahiro how to handle this, but I don't see any good
> justification to have ACPI (compile time) dependency here. So, again
> NAK!

Please tell me how this driver will be probed when CONFIG_ACPI
is disabled (it cannot, as nothing instantiates platform devices of the
right type, so there is no reason to bother the user with a question about
this driver when configuring his kernel).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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