[U-Boot] u-boot retries with fallback to other images

[Brendan Simon (eTRIX)]

Hi Wolfgang,

On 7/12/2015 5:23 PM, Wolfgang Denk wrote:
> Dear Brendan,
>
> In message <5663B74E.7000204 at etrix.com.au> you wrote:
>> Is there any documentation or u-boot support for having a list of boot
>> images to try, starting with the first in the list, trying 1, 2 or 3
>> times, then trying the next in the list.
>>
>> e.g. boot kernel at mmcblk0p3, then mmcblk0p2, then mmcblk1p2, then
>> tftp/nfs last resort fallback ?
>> or
>>     boot off partition 3 of eMMC, then partition2 of eMMC, then
>> partition 2 of SD card, then tftp/nfs ?
> Define a set of boot commands, say bootcmd1, bootcmd2, ...
> and then simply do
>
> 	run bootcmd1; run bootcmd2; ...
>
> The furst one that succeeds will not return.
>
> Note that the key problem with such a simplistic approach is that it
> will not help you in case an image looks OK, but hangs during boot -
> in that case, you need a watchdow and support for the bootcount
> feature.
>
> Best regards,
> Wolfgang Denk

Yes, the watchdog and bootcount feature is the advanced stuff I'm
looking for.
I would think this has been implemented numerous times, and I didn't
want to reinvent the wheel if there was some commonly used
infrastructure to support this.
If software does boot, then at some stage would set a u-boot variable to
say everything booted ok, so that it can be used again on next boot.

My use case is not that uncommon -- lots of embedded devices installed
in remote locations that are not easily accessible, but require remote
monitor and software updates.

Is there anything that is "standard" in u-boot to support this?
Or any work that is published that has attempted this?

Thanks,
Brendan.