Re: [PATCH RESEND v2 1/4] HID: hid-appletb-bl: add driver for the backlight of Apple Touch Bars

[Aditya Garg <gargaditya08@live.com>]

> On 4 Feb 2025, at 7:47 AM, Jiri Kosina <jikos@kernel.org> wrote:
> 
> On Tue, 4 Feb 2025, Aditya Garg wrote:
> 
>> You might have noticed that the hid-apple driver has code for the magic
>> backlight. Now we have a case of MacBook Air 2020, which does not have a
>> touchbar but still shows presence of the touchbar backlight device, just
>> because it needs it for the keyboard backlight. In case we merge both
>> the backlight and touchbar code in a driver, on that model, the
>> backlight breaks. If kept separate, the touchbar driver simply doesn't
>> load and backlight works.
> 
> Sorry for being dense, but does that mean that it's either hid-appletb-bl
> or hid-apple, but never both to make a good user experience on those
> devices?
> 
> If so, can you please point out what exactly is the reason?
> 
> Either those have different VID/PID combination, and then it can be easily
> made conditional both in code and in runtime.
> Are we talking about conflicting VID/PID combinations, some of them
> needing current hid-apple, and some of them needing (in a mutually
> exclusive way) hid-appletb-bl?
> 

The driver uses the 0th interface for managing the touchbar and the 1st interface for backlight, but there is no touchbar on MacBook Air 2020, so the 0th interface is used for backlight on that.

I remember the author trying various combinations, but having a separate driver was the most feasible option, both for backlight, and the drivers for windows and macOS mode.

> Thanks,
> 
> --
> Jiri Kosina
> SUSE Labs
>