Fairly minimal sdcard content for booting kernel and world on an RPI2 V1.1 from a USB SSD instead of from the sdcard [corrections]

[Ian Lepore]

On Sat, 2017-12-23 at 16:40 -0800, Mark Millard wrote:
> It does not appear that a fixed loaderdev
> definition can even be used to pick out
> the MMC (or any other specific device)
> unless what else is connected is also
> controlled (stable properties from boot
> to boot).

As usual, I find it basically impossible to read your wall of text.  I
did notice that paragraph while trying to skim through it.  

If you want to select an MMC device regardless of what USB devices may
be present, set loaderdev to mmc, mmc0, mmc1, etc.  If there are
multiple mmc devices which may or may not be present, there's not much
you can do, because if no card is present in the slot uboot normally
assigns to mmc0, then any card in the other slot will become mmc0.  The
same applies to other device types such as sata and usb, you can name
the type, but uboot will always just number whatever is present
starting at 0 without regard to the physical
slot/port/location/whatever.

-- Ian