SPI CS configuration for P9.23 on AM572xx, kernel 4.19

Created by: dmconover

I have been working on adapting an industrial application from the BeagleBone Black to the AI and came across the v4.19.x-ti-overlays branch of the Beagleboard Device Trees repo. Thanks to the great work done here already, I was able to properly configure CAN,UART,etc fairly easily! However, one necessery step I need is to configure P9.23 as a SPI chip select pin. According to the BeagleBone Cape Header Spreadsheet (cell BT58, specifically), this should be an option for pin configuration. However, this doesn't seem to be an option in am572x-bone-common-univ.dtsi, and if I try to add it myself, the resulting overlay will brick my device. I was wondering if someone better acquainted with this project had any ideas about how to add this functionality into the v4.19.x-ti-overlays branch. The resulting option would appear as something like:

• P9_23_spi_cs_pin: pinmux_P9_23_spi_cs_pin { pinctrl-single,pins = <
  P9_23( PIN_OUTPUT_PULLUP | INPUT_EN | MUX_MODE3)>; };

If someone could even point me in the right direction, I'd be happy to try to implement it myself!

Thanks,

Doug