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 17:57:39 +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 5:53 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
> On 1/25/2018 11:47 AM, Rafael J. Wysocki wrote:
>> 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?
>
> That was the original patch. Folks are saying that it breaks some systems.
>
> Conversation is here:
>
> https://patchwork.kernel.org/patch/10142425/

Couldn't that be addressed by preventing the I2C module from being
unloaded in the relevant cases?