Synaptics LED support

[Peter Hutterer]

On Mon, Mar 09, 2015 at 10:44:36PM +0300, George Sedov wrote:
> Hi all,
> 
> Some synaptics touchpads have a LED embedded to the upper-left corner,
> which is supposed to be used to disable the touchpad by double-tapping
> it. In linux, the proper support for it was never mainlined.
> 
> There were a couple of out-of-tree patches (can be found here
> https://github.com/perusio/xorg-synaptics-led-support) which supposedly
> came from SUSE enterprise, but they were never really finished. One of
> the two patches is for the kernel, to support the LED itself, and the
> other one for the Xorg driver, to support the double tap.
> 
> The Xorg driver relied on the kernel to distinguish the supported
> devices (double tap worked if the sys-file for the LED was present), and
> the kernel should have relied on the device properties to distinguish
> them, but that part was the one that  was never finished. The particular
> device ID was inserted instead, which made the driver useless for all
> but one touchpad models.
> 
> Is there any chance this LED functionality can be supported in libinput?
> What can be done about it? Maybe I can be of some help. I would really
> love to see this functionality in linux, even if 4 years later.

first: yes, unlike synaptics, libinput could support this since it'd be
nicely hidden away in libinput, only apply to specific models, etc.

what I'm more concerned about: if it's 4 years later - how many devices
still have that functionality? I'm hesitant to add a feature that only works
on laptops that have been discontinued a significant amount of time ago.

Cheers,
   Peter