Re: [PATCH] ACPI: video: Don't allow MFD devices to probe

[Mario Limonciello <superm1@kernel.org>]

On 3/6/26 6:17 AM, Rafael J. Wysocki wrote:
> On Fri, Mar 6, 2026 at 11:50 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>>
>> On Fri, Mar 6, 2026 at 3:51 AM Mario Limonciello (AMD)
>> <superm1@kernel.org> wrote:
>>>
>>> After ACPI video was converted into a platform device in
>>> commit 02c057ddefef5 ("ACPI: video: Convert the driver to a platform one")
>>> other devices that are MFD children of LNXVIDEO are being probed.
>>> This isn't intended.
>>>
>>> During probe detect MFD cells and reject them.
>>>
>>> Fixes: 02c057ddefef5 ("ACPI: video: Convert the driver to a platform one")
>>> Reported-by: Pratap Nirujogi <pnirujog@amd.com>
>>> Closes: https://lore.kernel.org/regressions/007e3390-6b2b-457e-83c7-c794c5952018@amd.com/
>>
>> The link is broken, so I can't see what is really happening, but my
>> guess is that MFD devices are created under the video bus device and
>> they get the same device ID (confusingly enough).

Hmm, I just double checked the link and it worked for me.

But you are on the To: list of that thread also.

>>
>>> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
>>> ---
>>>   drivers/acpi/acpi_video.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
>>> index 3fa28f1abca38..2cb526775ac47 100644
>>> --- a/drivers/acpi/acpi_video.c
>>> +++ b/drivers/acpi/acpi_video.c
>>> @@ -14,6 +14,7 @@
>>>   #include <linux/init.h>
>>>   #include <linux/types.h>
>>>   #include <linux/list.h>
>>> +#include <linux/mfd/core.h>
>>>   #include <linux/mutex.h>
>>>   #include <linux/input.h>
>>>   #include <linux/backlight.h>
>>> @@ -1988,6 +1989,9 @@ static int acpi_video_bus_probe(struct platform_device *pdev)
>>>          int error;
>>>          acpi_status status;
>>>
>>> +       if (mfd_get_cell(pdev))
>>> +               return -ENODEV;
>>
>> If the above is the case, I'd prefer this check
>>
>>          if (!device->pnp.type.backlight)
>>
>> which should also work, but is more general.
> 
> Well, this will not work if the ACPI companion is shared between
> multiple devices.
> 
> However, adding an MFD check here is a "works for me" change rather.
> 
> I think what needs to be done is to extend the duplication check (see
> my patch from yesterday at
> https://lore.kernel.org/linux-acpi/5663583.Sb9uPGUboI@rafael.j.wysocki/)
> to detect the cases when another platform device (not necessarily a
> child of the same parent) sharing the same ACPI companion is probed.
> 

Generally makes sense to me.  But in this particular case it shouldn't 
be a FW_BUG.

Do you want to roll this in your series?  Or would you prefer one of us 
to send a follow up patch?