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Date:   Thu, 22 Sep 2022 15:48:07 +0200
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Subject: Re: [PATCH -next 1/2] i2c: designware: Switch from using MMIO access
 to SMN access
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To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Borislav Petkov <bp@suse.de>
Cc:     "Limonciello, Mario" <mario.limonciello@amd.com>,
        =?UTF-8?B?SmFuIETEhWJyb8Wb?= <jsd@semihalf.com>,
        linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
        jarkko.nikula@linux.intel.com, wsa@kernel.org,
        rrangel@chromium.org, upstream@semihalf.com,
        Muralidhara M K <muralimk@amd.com>,
        Naveen Krishna Chatradhi <nchatrad@amd.com>
References: <20220916131854.687371-1-jsd@semihalf.com>
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 <eafc7bb5-a406-132b-4b7d-167917cdab05@amd.com>
 <CAOtMz3Pgh+cERiXVetDZJrQa9C0kUUbZ9dRRhdghgm5Or8kwhg@mail.gmail.com>
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 <Yyt5LSxSz+6QeWF1@zn.tnic> <YywvmueFj/ibyZdf@smile.fi.intel.com>
 <YywwEvkZK1R9mJfE@smile.fi.intel.com>
From:   Hans de Goede <hdegoede@redhat.com>
In-Reply-To: <YywwEvkZK1R9mJfE@smile.fi.intel.com>
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Hi,

On 9/22/22 11:51, Andy Shevchenko wrote:
> +Cc: Hans (mentioned your name and was under impression that you are in Cc list already)
> 
> On Thu, Sep 22, 2022 at 12:49:15PM +0300, Andy Shevchenko wrote:
>> On Wed, Sep 21, 2022 at 10:50:53PM +0200, Borislav Petkov wrote:
>>> On Wed, Sep 21, 2022 at 03:19:26PM -0500, Limonciello, Mario wrote:
>>>> Jan mentioned this in the commit message:
>>>>
>>>>> The function which registers i2c-designware-platdrv is a
>>>>> subsys_initcall that is executed before fs_initcall (when enumeration > of
>>>> NB descriptors occurs).
>>>>
>>>> So if it's not exported again, then it means that we somehow
>>>> need to get i2c-designware-platdrv to register earlier too.
>>>
>>> So I have this there:
>>>
>>> /* This has to go after the PCI subsystem */
>>> fs_initcall(init_amd_nbs);
>>>
>>> as I need PCI. It itself does
>>>
>>> arch_initcall(pci_arch_init);
>>>
>>> so I guess init_amd_nbs() could be a subsys_initcall...
>>>
>>> Or why is
>>>
>>> subsys_initcall(dw_i2c_init_driver);
>>>
>>> a subsys initcall in the first place?
>>>
>>> Looking at
>>>
>>>   104522806a7d ("i2c: designware: dw_i2c_init_driver as subsys initcall")
>>>
>>> I don't see a particular reason why it should be a subsys_initcall...
>>>
>>> In any case, this should be fixed without an export which was crap in
>>> the first place.
>>>
>>> Hm.
>>
>> I'm speculating here, but IIRC the I2C controllers may serve PMICs on some
>> platform that are required to be present earlier due to some ACPI code
>> accessing them. This Hans de Goede can confirm or correct me.

Right, thank you for Cc-ing me. At least on X86 there are several platforms
(and 100-s of device models) which use a PMIC connected to the i2c-designware
controller and this PMIC gets poked directly from ACPI _S0 and _S3
(power on/off) methods. So the I2C bus driver needs to *bind* to the controller
as soon as we find its description in ACPI, otherwise we get a whole bunch
of failed ACPI OpRegion access errors as well as various actual really issues.

So please keep this as a subsys initcall.

Regards,

Hans