[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[Leon Woestenberg]

Hello Wolfgang,

On Thu, May 29, 2008 at 12:41 AM, Wolfgang Denk <wd at denx.de> wrote:
> in message <c384c5ea0805281514r1740072fw7c49101a4535f818 at mail.gmail.com> you wrote:
>>
>> For how long can I expect current u-boot (say 1.3.4) to be forward
>> compatible with newer Linux kernels?
>
> I think chances are pretty good. Please keep in mind that we're right
>
> But even today you can build a current Linux kernel using the cuImage
> wrapper and boot it on an old (say, version 1.2.0) U-Boot.
>
Thanks for your clear answer, takes away my cloud of doubt.

>> Also, is there any plan to add fail-safe features to u-boot?
>
> What are you thinking of?
>
My main requirement is to have the bootloader make a decision to boot
a fall back image in case the normal image does not boot (for whatever
reason). The fall back image is a user friendly way to unbrick the
device. It itself is never overwritten. (In my case a web server with
firmware upgrade Java applet, for example).

Currently, my flow is as follows (with implementation in redboot)

boot loader:
enable hardware watchdog
if flag A is set
  clear flag A
  load normal image, boot
  else if the normal image was not loaded, boot fallback.
else
  boot fallback

the normal image sets flag A when it wants to reboot, then stops
servicing the watchdog and resets

if normal image either did not set flag A (it crashes) or it did not
service the watchdog, the watchdog will reset the board.

I wonder if this is a common use and if it makes sense to implement
this for mainstream u-boot, or is this very specific?

Regards,
-- 
Leon