Don't working touchpad #50

The trackpad should work if it is properly GPIO pinned, but it may be timing out when falling back to I2C interrupts.

Essentially what this means is that instead of using GPIO -- an event-based system (where messages are only sent to and from the CPU as needed) -- instead, the trackpad driver may be falling back to polling messages from the trackpad at a regular interval.

If the trackpad is somehow misconfigured, polling over I2C will not receive any responses from the trackpad. You can check for this behavior with sudo dmesg | grep -i Voodoo to spot any messages like these:

[  155.146947]: VoodooI2CControllerDriver::pci8086,2eb I2C Transaction error details
[  155.146967]: VoodooI2CControllerDriver::pci8086,2eb slave address not acknowledged (7bit mode)
[  155.146971]: VoodooI2CControllerDriver::pci8086,2eb I2C Transaction error: 0x0b800001 - aborting

You'll want to add msgbuf=1048576 to your config.plist's boot-args (under NVRAM -> Add -> 7C436110-AB2A-4BBB-A880-FE41995C9F82), which will expand the buffer size for dmesg. This will prevent logs from being truncated, as the default size is very small and is likely to be overwritten very quickly.

You'll also want to grab some more detailed information about what hardware is detected for the VoodooI2C drivers by running the below command (example output):

ioreg -rxn IOHIDInterface -k "VoodooI2CServices Supported" -t | grep -E 'IOACPIPlatformDevice|IOPCIDevice|VoodooI2CDeviceNub|VendorID|ProductID|HIDEventDriver  <class VoodooI2C|Interface  <class VoodooI2C' | cut -d "<" -f1