Backwards compatiblity for QorIQ FMAN LIODN entries

[Hamish Martin <Hamish.Martin@alliedtelesis.co.nz>]

Hi Rob and Mark,

I am upgrading the kernel on a Freescale P2040 based system and have
struck an issue with LIODNs not being updated by uboot for an FMAN
ethernet port.

My system has an old uboot running which fails in its attempt to update
the fman rx port node with the required LIODN entry. This is because my
old uboot installation is looking for compatibility value "fsl,fman-
port-1g-rx" while the latest kernel defines the compatible value as
"fsl,fman-v2-port-rx" (see for
instance arch/powerpc/boot/dts/fsl/qoriq-fman-0-1g-3.dtsi).
Newer uboot looks for both values per this commit:
https://github.com/u-boot/u-boot/commit/97a8d010e029111e5711a45264a726b
edbeb24c4#diff-43243b910837283bb1d5d626f4d89d75

I am unable to update bootloaders for devices of this type in the field
so I am wondering if the correct approach is to adjust my DTS file
locally to add the compatible string my old uboot is searching for, or
if we should add this to the various qoriq-fman dtsi files in the
kernel to make this work in a nice backwards compatible way.

Let me know your opinion. I'm happy to work up a patch if you'd like to
make the change in the kernel, otherwise I'll handle it locally by
overriding the compatible string in my system's dts file.

Thanks,
Hamish M