linux-kernel - Re: [RFC 03/32] ACPI: Kconfig: add HAS

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Date:   Tue, 28 Dec 2021 16:20:02 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        John Garry <john.garry@...wei.com>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        linux-riscv@...ts.infradead.org, linux-csky@...r.kernel.org,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [RFC 03/32] ACPI: Kconfig: add HAS_IOPORT dependencies

On Mon, Dec 27, 2021 at 6:43 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
>
> On Mon, 2021-12-27 at 18:15 +0100, Rafael J. Wysocki wrote:
> > On Mon, Dec 27, 2021 at 6:12 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > > On Mon, Dec 27, 2021 at 6:02 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
> > > > On Mon, 2021-12-27 at 17:47 +0100, Rafael J. Wysocki wrote:
> > > > > On Mon, Dec 27, 2021 at 5:44 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
> > > > > > In a future patch HAS_IOPORT=n will result in inb()/outb() and friends
> > > > > > not being declared. As ACPI always uses I/O port access
> > > > >
> > > > > The ARM64 people may not agree with this.
> > > >
> > > > Maybe my wording is bad. This is my rewording of what Arnd had in his
> > > > original mail: "The ACPI subsystem needs access to I/O ports, so that
> > > > also gets a dependency."(
> > > > https://lore.kernel.org/lkml/CAK8P3a0MNbx-iuzW_-=0ab6-TTZzwV-PT_6gAC1Gp5PgYyHcrA@mail.gmail.com/
> > > > ).
> > >
> > > And my point is that on ARM64 the ACPI subsystem does not need to
> > > access IO ports.
> > >
> > > It may not even need to access them on x86, but that depends on the
> > > platform firmware in use.
>
> Well at least it does compile code calling outb() in
> drivers/acpi/ec.c:acpi_ec_write_cmd().

That's the EC driver which is not used on arm64 AFAICS and that driver
itself can be made depend on HAS_IOPORT.

> Not sure if there is an
> alternative path at runtime if there is then we might want to instead
> use ifdefs to always use the non I/O port path if HAS_IOPORT is
> undefined.
>
> > >
> > > If arm64 is going to set HAS_IOPORT, then fine, but is it (and this
> > > applies to ia64 too)?
>
> Yes x86, arm64 and ia64 that is all arches that set ACH_SUPPORTS_ACPI
> all select HAS_IOPORT too. See patch 02 or the summary in the cover
> letter which notes that only s390, nds32, um, h8300, nios2, openrisc,
> hexagon, csky, and xtensa do not select it.

If that is the case, there should be no need to add the extra
dependency to CONFIG_ACPI.

> > >
> > > > > > we depend on HAS_IOPORT unconditionally.
> > > > > >
> > > > > > Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> > > > > > Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> > > > > > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > > > > > ---
> > > > > >  drivers/acpi/Kconfig | 1 +
> > > > > >  1 file changed, 1 insertion(+)
> > > > > >
> > > > > > diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> > > > > > index cdbdf68bd98f..b57f15817ede 100644
> > > > > > --- a/drivers/acpi/Kconfig
> > > > > > +++ b/drivers/acpi/Kconfig
> > > > > > @@ -9,6 +9,7 @@ config ARCH_SUPPORTS_ACPI
> > > > > >  menuconfig ACPI
> > > > > >         bool "ACPI (Advanced Configuration and Power Interface) Support"
> > > > > >         depends on ARCH_SUPPORTS_ACPI
> >
> > Besides, I'm not sure why ARCH_SUPPORTS_ACPI cannot cover this new dependency.
>
> If you prefer to have the dependency there that should work too yes.

I would prefer that.

IMO, if ARCH_SUPPORTS_ACPI is set, all of the requisite dependencies
should be met.