linux/Documentation/devicetree/bindings/serial/omap_serial.txt
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   1OMAP UART controller
   2
   3Required properties:
   4- compatible : should be "ti,omap2-uart" for OMAP2 controllers
   5- compatible : should be "ti,omap3-uart" for OMAP3 controllers
   6- compatible : should be "ti,omap4-uart" for OMAP4 controllers
   7- ti,hwmods : Must be "uart<n>", n being the instance number (1-based)
   8
   9Optional properties:
  10- clock-frequency : frequency of the clock input to the UART
  11