linux-kernel - Re: [PATCH] platform/x86: lenovo-hotkey: Handle missing hardware features gracefully

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Message-ID: <fb08672d-881b-458c-b8ed-1a27ca93fe7d@gmx.de>
Date: Fri, 27 Jun 2025 23:17:36 +0200
From: Armin Wolf <W_Armin@....de>
To: Kurt Borja <kuurtb@...il.com>, xy-jackie@....com,
 alireza.bestboyy@...il.com, atescula@...il.com
Cc: mpearson-lenovo@...ebb.ca, hdegoede@...hat.com,
 ilpo.jarvinen@...ux.intel.com, platform-driver-x86@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform/x86: lenovo-hotkey: Handle missing hardware
 features gracefully

Am 27.06.25 um 22:38 schrieb Kurt Borja:

> Hi Armin,
>
> On Fri Jun 27, 2025 at 4:54 PM -03, Armin Wolf wrote:
>> Not all devices support audio mute and microphone mute LEDs, so the
>> explicitly checks for hardware support while probing. However missing
>> hardware features are treated as errors, causing the driver so fail
>> probing on devices that do not support both LEDs.
>>
>> Fix this by simply ignoring hardware features that are not present.
>> This way the driver will properly load on devices not supporting both
>> LEDs and will stop throwing error messages on devices with no LEDS
>> at all.
> This patch makes me wonder what is the policy around issues like this.
> In fact I've submitted and changes that do the exact opposite :p
> Like commit: 4630b99d2e93 ("platform/x86: dell-pc: Propagate errors when
> detecting feature support")
>
> IMO missing features should be treated as errors. i.e. The probe should
> fail.

IMHO the probe should only fail if some features are deemed essential, like
required ACPI methods. Optional features like in this case LEDs should be
handled by the driver in a graceful manner if possible.

>
> Quoting documentation [1]:
>
> 	If a match is found, the device’s driver field is set to the
> 	driver and the driver’s probe callback is called. This gives the
> 	driver a chance to verify that it really does support the
> 	hardware, and that it’s in a working state.
>
> And again [2]:
>
> 	This callback holds the driver-specific logic to bind the driver
> 	to a given device. That includes verifying that the device is
> 	present, that it’s a version the driver can handle, that driver
> 	data structures can be allocated and initialized, and that any
> 	hardware can be initialized.
>
> Both of these makes me wonder if such a "fail" or error message should
> be fixed in the first place. In this case the probe correctly checks for
> device support and fails if it's not found, which is suggested to be the
> correct behavior.

The driver should only fail probing if it cannot handle some missing features.
In this case however both features (audio mute LED and mic mute LED) are completely
optional and the driver should not fail to load just because one of them is absent.

Just think about machines supporting only a single LED (audio or mic mute). Currently
the driver would fail to load on such devices leaving the users with nothing.

>
> BTW this also leaks `wpriv`, which would remain allocated for no reason.

wpriv will be freed using devres, so no memory leak here. However i admit that there is
some room for optimizations, however i leave this to the maintainer of the driver in
question.

Thanks,
Armin Wolf

>
>
> [1] https://docs.kernel.org/driver-api/driver-model/binding.html
> [2] https://docs.kernel.org/driver-api/driver-model/driver.html
>