Re: [External] Re: Dell laptop touchpad disabling?

[Hans de Goede <hdegoede@redhat.com>]

Hi Mark,

On 3/21/22 23:18, Mark Pearson wrote:
> 
> Apologies if this is thread hijacking...but I've got a similarish
> problem on Lenovo laptops that we have on the todo list to investigate
> so wanted to jump in with a somewhat related question...

No problem.

> On 3/18/22 04:54, Hans de Goede wrote:
>>
>> Regardless of the method, the kernel's responsibility here is
>> to make sure the touchpad gets seen as a touchpad and after that
>> "disabling" it is a userspace problem.
>>
> 
> The issue on our platforms is that if you disable the touchpad in the
> BIOS it doesn't actually disable the touchpad. It sets a flag in the EC
> registers to let the OS know the touchpad is not supposed to be enabled
> (I only just found out this is how it is supposed to work).

Interesting.

> I'm not 100% sure the reasons for this - I think it's to do with keeping
> the trackpoint usable (maybe).

Yes that makes sense the trackpoint often sends its data to the touchpad
which then muxes the trackpoint data into its own datastream as special
trackpoint packets. So disabling the touchpad at the hw level would also
disable the trackpoint in these kinda setups.

> So just curious on the comment above - is there a standard way to let
> user space know to ignore the touchpad or disable it by default?

Not yet, but we could define one. Or we could even try to see if
a patch to drop all non trackpoint data inside the kernel when the
flag is set would be accepted.

Someone needs to write the code for this though and if we want to let
userspace know also define a userspace API. I think the all kernel
solution might be the easiest to implement, but I'm not sure if this
will be accepted by the input subsystem maintainer.

> I'm obviously being lazy here as I've been meaning to go and read code
> but I was flicking thru the mailing list and this caught my eye....and
> if there's a shortcut to the answer that would be awesome.
> 
> I've no idea if this is a Lenovo specific issue or more generic - but
> this thread made me wonder if it's actually a common/standard problem?

This is the first time I have heard about this.

Regards,

Hans