This driver supports I2C HID devices connected to Intel LPSS I2C controllers
from Tiger Lake on.

Configuration
~~~~~~~~~~~~~

Some properties of the used device must be configured via '<config>'
attributes as the default configuration is tailored to Fujitsu LIFEBOOK
U7411 with Synaptics touchpad.

The default configuration is like follows.

! <config>
!   <i2c_slave irq="266" bus_addr="44" hid_addr="32" gpio_chip="INT34C5"/>
!   <i2c_master bus_speed_hz="400000">
!     <fmcn hcnt="193" lcnt="313" hold_time="80"/>
!     <sscn hcnt="500" lcnt="588" hold_time="80"/>
!   </i2c_master>
! </config>

I2C client configuration
------------------------

The '<i2c_slave>' node is used to configure how the HID device is reached via
I2C with the following attributes.

:gpio_chip: If the device is connected to a GPIO pin in interrupt mode, the
  driver needs to know the name of the GPIO controller device.

:irq: The interrupt number (GPIO pin or IO-APIC) used for requesting
  input-event handling.

:bus_addr: The I2C bus address of the concrete controllers differs among
  touchpad manufacturers and can be adjusted via this attribute.

:hid_addr: The I2C register address of the HID descriptor is reflected via
  ACPI device-specific methods (which are not supported yet) and can be
  explicitly configured with this attribute.

I2C master configuration
------------------------

The '<i2c_master>' node defines timing properties used by the Designware
I2C controller. Since we have no mechanism for extracting these values from
ACPI tables (yet), we resort to explicit configuration.

:bus_speed_hz: The I2C bus frequency in Hz.

The node may contain a '<fmcn>' (Fast Mode, 400KHz) and a
'<sscn>' (Standard Mode, 100KHz) node. Each of those supports the following
attributes.

:hcnt: Value of the designware I2C controller's high count register.

:lcnt: Value of the designware I2C controller's low count register.

:hold_time: SDA hold time parameter.
