ChromeOS Embedded Controller

modulename: cros_ec.ko

configname: CONFIG_MFD_CROS_EC

Linux Kernel Configuration
└─>Device Drivers
└─>Multifunction device drivers
└─>ChromeOS Embedded Controller
In linux kernel since version 3.1 (release Date: 2011-10-24)  
If you say Y here you get support for the ChromeOS Embedded
Controller (EC) providing keyboard, battery and power services.
You also ned to enable the driver for the bus you are using. The
protocol for talking to the EC is defined by the bus driver.

source code:
selects
CONFIG_MFD_CORE


is selected by
CONFIG_SND_SOC_SDM845