tried to diff with the config and, as you suspected, it wasn't too useful as there were many differences. I did find that CONFIG_MFD_AT91_USART was defined
$this->bbcode_second_pass_code('', '...
#
# Multifunction device drivers
#
CONFIG_MFD_CORE=y
# CONFIG_MFD_ACT8945A is not set
# CONFIG_MFD_AS3711 is not set
# CONFIG_MFD_AS3722 is not set
# CONFIG_PMIC_ADP5520 is not set
# CONFIG_MFD_AAT2870_CORE is not set
CONFIG_MFD_AT91_USART=y
# CONFIG_MFD_ATMEL_FLEXCOM is not set
CONFIG_MFD_ATMEL_HLCDC=y
CONFIG_MFD_ATMEL_SMC=y
# CONFIG_MFD_BCM590XX is not set
# CONFIG_MFD_BD9571MWV is not set
# CONFIG_MFD_AXP20X_I2C is not set
# CONFIG_MFD_MADERA is not set
# CONFIG_MFD_ASIC3 is not set
# CONFIG_PMIC_DA903X is not set
# CONFIG_MFD_DA9052_SPI is not set
# CONFIG_MFD_DA9052_I2C is not set
# CONFIG_MFD_DA9055 is not set
# CONFIG_MFD_DA9062 is not set
# CONFIG_MFD_DA9063 is not set
# CONFIG_MFD_DA9150 is not set
...
')
I figure it's might be easier to look at the full config so I have uploaded it here :
https://gist.githubusercontent.com/Jess ... tfile1.txt