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

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Date:   Thu, 25 Jan 2018 17:47:25 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     "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>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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 Thu, Jan 25, 2018 at 5:32 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
> On 1/25/2018 11:25 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 AFAIC>
>> OTOH, there are systems using ACPI without I2C opregions, so are we
>> really better off by forcing everybody using ACPI to also build I2C?
>
> I was trying to find a good balance by choosing imply instead of select.
>
> If an OS chooses to include an I2C driver as a module (most distros do),
> core-i2c functionality becomes a built-in module with ACPI.

So what would be wrong with allowing ACPI_I2C_OPREGION to be set if
I2C is a module?