Kernel 3.14 and UART4


when changing from Kernel 3.8 to 3.14 I discovered that UART4 was not working anymore. With Kernel 3.8 I was able to enable it in uEnv.txt using “cape_enable=capemgr.enable_partno=BB-UART4”. So I checked the device tree configuration as described here and was able to enable UART4 setting “dtb=am335x-boneblack-ttyO4.dtb” in uEnv.txt. Comparing am335x-boneblack-ttyO4.dts with am335x-boneblack.dts I can see that *-tty04.dts includes am335x-bone-ttyO4.dtsi instead of am335x-ttyO4.dtsi.
My question is: What is the purpose of splitting this up into the two files am335x-bone-ttyO4.dtsi and am335x-ttyO4.dtsi? Why is am335x-boneblack.dts including am335x-ttyO4.dtsi and not am335x-bone-ttyO4.dtsi (which is actually commented out)? I just would like to understand the idea behind this structure.

Thanks and best regards