linux-kernel - Re: [PATCH v3] ACPI: Force I2C to be selected as a built-in module

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Date:   Thu, 08 Feb 2018 10:52:57 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Timur Tabi <timur@...eaurora.org>,
        Eric Auger <eric.auger@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] ACPI: Force I2C to be selected as a built-in module

On Tuesday, February 6, 2018 3:25:58 PM CET Sinan Kaya wrote:
> Hi Rafael,
> 
> On 1/25/2018 12:36 PM, Randy Dunlap wrote:
> > On 01/25/2018 08:25 AM, Rafael J. Wysocki wrote:
> >> On Thu, Jan 25, 2018 at 4:43 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
> >>> From: Auger Eric <eric.auger@...hat.com>
> >>>
> >>> If I2C is built as a module, ACPI_I2C_OPREGION cannot be set
> >>> and any ACPI opregion calls targeting I2C fail with no opregion found.
> >>>
> >>> Commit da3c6647ee08 ("I2C/ACPI: Clean up I2C ACPI code and Add
> >>> CONFIG_I2C_ACPI config") says following:
> >>>
> >>> "Current there is a race between removing I2C ACPI operation region
> >>> and ACPI AML code accessing."
> >>>
> >>> This patch forces core I2C support to be compiled as a built-in
> >>> module if ACPI is selected as code is not ready for dynamic module
> >>> removal.
> >>>
> >>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> >>> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> >>> ---
> >>>  drivers/acpi/Kconfig | 2 ++
> >>>  1 file changed, 2 insertions(+)
> >>>
> >>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> >>> index 4650539..5b48098 100644
> >>> --- a/drivers/acpi/Kconfig
> >>> +++ b/drivers/acpi/Kconfig
> >>> @@ -9,6 +9,8 @@ menuconfig ACPI
> >>>         depends on IA64 || X86 || ARM64
> >>>         depends on PCI
> >>>         select PNP
> >>> +       # force building I2C in on ACPI systems, for opregion availability
> >>> +       imply I2C
> >>>         default y if (IA64 || X86)
> >>>         help
> >>>           Advanced Configuration and Power Interface (ACPI) support for
> >>> --
> >>
> >> I'm not sure how much this helps.
> >>
> >> I2C opregions will only work if the requisite I2C controller driver is
> >> present anyway and this change doesn't guarantee that AFAICS.
> >>
> >> OTOH, there are systems using ACPI without I2C opregions, so are we
> >> really better off by forcing everybody using ACPI to also build I2C?
> > 
> > Definitely not.
> > 
> 
> Where do we stand on this? Do you have a better suggestion?

Not at the moment, but I also don't think that this approach is valid.

Thanks,
Rafael