[U-Boot] [RFC] Improve bootargs for IGEP boards.

[Enric Balletbo Serra]

Now that all the IGEP boards have Device Tree support and uImage is
deprecated in favour of zImage, maybe, it's time to rethink the
default boot command. We can also use this to unify the different
bootargs between IGEP0020/30/32 and IGEP0033 that now are a bit
different.

IMHO, basically, there are two uses cases that must complain the
default bootargs: Booting from a SD-card and booting from Flash.

Below, I present different options and I would like people opine to
select the best.

BOOT FROM SD-CARD

 o 1st proposal:

    Two partition with following files:
        - boot (FAT) : MLO + u-boot.img + zImage + dtb files + uEnv.txt
        - rootfs (ext2/3/4) : filesystem + kernel modules.
    The rootfs can mount the boot partition to /boot

  o 2nd proposal:

    Two partitions with following files:
        - boot (FAT) : MLO + u-boot.img
        - rootfs (ext2/3/4) : zImage + dtb files + uEnv.txt + kernel
modules + filesystem

BOOT FROM NAND:

  o 1st proposal: (the traditional layout)

    5 partitions:
        SPL
        U-Boot
        U-Boot Environment
        Kernel (raw)
        Rootfs

    With a Device Tree kernel the problem is that we should use the
kernel with appended dtb file or load the dtb file from rootfs. And if
we need to load the dtb file from the rootfs, why not load the kernel
also ?

  o 2nd proposal:

    4 partitions:
        SPL
        U-Boot
        U-Boot Environment
        Filesystem (ubifs): zImage + kernel modules + dtbs files + filesystem

So, what do you think is the best approach to be the default
environment ? Better layouts ? Advantages - disadvantages for every
layout ? Opinions are welcome.

Thanks in advance,
   Enric