linux-kernel - Re: [PATCH] platform/x86: thinkpad_acpi: Fix registration of tpacpi platform driver

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Message-Id: <be3804af-339a-4b5b-927a-06d98dfadc11@app.fastmail.com>
Date: Sun, 09 Feb 2025 19:54:04 -0500
From: "Mark Pearson" <mpearson-lenovo@...ebb.ca>
To: "Kurt Borja" <kuurtb@...il.com>
Cc: "Hans de Goede" <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 "Limonciello, Mario" <mario.limonciello@....com>,
 "platform-driver-x86@...r.kernel.org" <platform-driver-x86@...r.kernel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform/x86: thinkpad_acpi: Fix registration of tpacpi platform
 driver

Hi Kurt,

On Sat, Feb 8, 2025, at 8:54 AM, Kurt Borja wrote:
> On Sat Feb 8, 2025 at 11:26 AM -05, Mark Pearson wrote:
>> Thanks Kurt,
>>
>> On Fri, Feb 7, 2025, at 11:56 PM, Kurt Borja wrote:
>>> Hi Mark,
>>>
>>> On Sat Feb 8, 2025 at 4:14 AM -05, Mark Pearson wrote:
>>>> When reviewing and testing the recent platform profile changes I had
>>>> missed that they prevent the tpacpi platform driver from registering.
>>>> This error is seen in the kernel logs, and the various tpacpi entries
>>>> are not created:
>>>> [ 7550.642171] platform thinkpad_acpi: Resources present before probing
>>>
>>> This happens because in thinkpad_acpi_module_init(), ibm_init() is
>>> called before platform_driver_register(&tpacpi_pdriver), therefore
>>> devm_platform_profile_register() is called before tpacpi_pdev probes.
>>>
>>> As you can verify in [1], in the probing sequence, the driver core
>>> verifies the devres list is empty, which in this case is not because of
>>> the devm_ call.
>>>
>>>>
>>>> I believe this is because the platform_profile driver registers the
>>>> device as part of it's initialisation in devm_platform_profile_register,
>>>> and the thinkpad_acpi driver later fails as the resource is already used.
>>>>
>>>> Modified thinkpad_acpi so that it has a separate platform driver for the
>>>> profile handling, leaving the existing tpacpi_pdev to register
>>>> successfully.
>>>
>>> While this works, it does not address the problem directly. Also it is
>>> discouraged to create "fake" platform devices [2].
>>>
>>> May I suggest moving tpacpi_pdriver registration before ibm_init()
>>> instead, so ibm_init_struct's .init callbacks can use devres?
>>>
>>
>> Yep - you're right. Moving it before the init does also fix it.
>>
>> I can't see any issues with this approach, but I'll test it out a bit more carefully and do an updated version with this approach.
>
> Thinking about it a bit more. With this approach you should maybe create
> the tpacpi_pdev with platform_create_bundle() (I'm pretty sure you can
> pass a NULL (*probe) callback) to avoid races.
>
> platform_create_bundle() only returns after the device has been
> successfully bound to the driver.
>
Unfortunately having a null probe callback doesn't work - you end up with an oops for a null pointer dereference.

Thanks
Mark