[U-Boot] Booting Wandboard through USB

[Stefano Babic <sbabic@denx.de>]

Hi Nikolay,

(jumping a little later in the discussion but trying to sumarize all
topics..)

IMHO we should find a way without constraining SPL to work differently
as thought only to allow loading from USB. For this reason I will tend
to a solution as much as possible "tools" only, that is extending
imx-usb-loader as try to bind together SPL and u-boot.bin and convince
SPL to load from memory. This becomes an artifact, because in the
reality, SPL loads from a storage.

On 01/06/2015 01:15, Nikolay Dimitrov wrote:
> 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

It looks like a straightforward solution. I guess that the USB-OTG
initialization is done as fallback when SPL cannot load from storage,
allowing us to have a single binary for "standard" booting and USB
booting. When load fails, USB is initialized.

> - 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.

Agree, this looks like a straight-forward solution.

> 
> 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?
> 


Best regards,
Stefano Babic


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