SMBus Trackpads about oc-little-translated HOT 3 CLOSED

Currently listed Trackpad IDs which support SMBus (according to Linux): https://github.com/torvalds/linux/blob/master/drivers/input/mouse/synaptics.c#L128-L194
Warning if trackpad potentially supports SMBus but is not listed: https://github.com/torvalds/linux/blob/master/drivers/input/mouse/synaptics.c#L1796-L1797
Where property is set in Synaptics VoodooPS2Trackpad: https://github.com/acidanthera/VoodooPS2/blob/master/VoodooPS2Trackpad/VoodooPS2SynapticsTouchPad.cpp#L390-L391

Elans check in VoodooPS2: https://github.com/acidanthera/VoodooPS2/blob/master/VoodooPS2Trackpad/VoodooPS2Elan.cpp#L211-L231
Note that with Elans, I think the PS2 driver is actually pretty good. Less need to use VoodooSMBus with it. Note that the Elans check requires Debug VoodooPS2, unlike the Synaptics check.

Edit:
Also, VoodooInput handles bridging info from VoodooPS2/I2C/RMI to macOS. It's main purpose is to spoof a Magic Trackpad 2 so that we get all the really nice gestures. VoodooPS2/RMI handle trackpoint hardware themselves. Generally, trackpoints aren't an important detail for users to worry so I'd focus on trackpads instead, since the trackpads are really what handle the trackpoint hardware.

i8042 = PS2 Controller
i801 = SMBus controller

Most Laptops hardware (For illustration purpose, I just show the PS2 side):

 _______     __________
| i8042 | - | Keyboard | (Kbd Port)
|       |   ------------
|       |    __________
|       | - | Trackpad |  (Mouse Port)
 -------    ------------
              |
           ____________
          | Trackpoint |  (PS2 Passthrough port on trackpad)
          --------------

The edge case here is HP, which likes to sometimes mux the Auxiliary/Mouse port on the i8042 controller. This means you'll have a case where the Trackpoint is connected directly to a PS2 port while the trackpad is connected to another PS2 port and the SMBus controller. It'll look more like (on the PS2 side):

 _______     __________
| i8042 | - | Keyboard | (Kbd Port)
|       |   ------------
|       |    __________
|       | - | Trackpad |   (Aux 0)
|       |   ------------
|       |    ____________
|       | - | Trackpoint |  (Aux 1)
|       |    -------------
|       | - (Aux 2)
|       | - (Aux 3)
--------

Acidanthera's VoodooPS2 is able to handle this edge case though, and will just attach VoodooPS2Mouse to the trackpoint.

from oc-little-translated.

Thanks for the explanations. I will correct it in the description and incorporate the info soon. As far as ThinkPads are concerned: I have a T530 which has an Ivy Bridge CPU but it doesn't use SMBus for the touchpad. So it's either it's not one of the many or SMBus really only became relevant from Haswell onward. Seems like there's a transition period between Ivy Bridge and Haswell. In the end it doesn't really matter because it has to be determined on a case by case basis anyway.

Since I don't have any other hardware to test all the stuff it's a drag really to collect all the info. Especially since almost every guide I could find is outdated and based on patching the DSDT.

from oc-little-translated.

A friend of mine has an HP with an SMBus trackpad and it's Ivy Bridge. It really is a case by case basis. Definitely not going to find any SMBus info in the DSDT as well. It's all determined by reading trackpad registers.

from oc-little-translated.