[U-Boot] Booting Wandboard through USB

[Nikolay Dimitrov <picmaster@mail.bg>]

Hi guys,

Here's a proposal how to avoid changing the host boot software for the
SPL case:

- Power on
- Boot ROM announces usb device (0x15a2:0x0054 or 0x15a2:0x0054 or
0x15a2:0x0063)
- Host software uploads SPL over OTG
- Board initializes DDR
- Board initializes USB-OTG and announces again as a usb device with
slightly different PID (0x15a2:0x0055 or 0x15a2:0x0056 or
0x15a2:0x0064) or a special PID (0x15a2:0xffff), thus needs to
implement FSL boot protocol
- Both imx-usb-loader and mfgtool already have easy mechanism to detect
boards' by vid-pid and to sequence actions based on it. So basically
we'll just need an additional config for the host boot programs, which
need to feed the 2nd boot stage (one more file for imx-usb-loader, and
one more config section for the mfgtool), but otherwise it will be
quite straight-forward.

Overall, from the PC host this boot sequence will look like 2 boot
sequences for 2 separate usb devices (1 for SPL, 1 for u-boot.img).

Probably the most important question is "how easy is to implement the
FSL boot protocol in the remaining OCRAM free space". What do you think?

Regards,
Nikolay