Failsafe booting to alternate linux image/fs

[Brendan Simon (eTRIX)]

I came across the "Boot Count Limit" feature in the U-Boot wiki, and it
looks like it will do exactly what I want.

    https://www.denx.de/wiki/view/DULG/UBootBootCountLimit


However, it also states that the "feature is available only for MPC8xx,
MPC82xx and MPC5200 Power Architecture® processors"

Is that accurate?  Is it not available for ARM processors (e.g. A9 CPU
system within Xilinx Zynq 7000 series SoCs) ?

Thanks, Brendan,

--

On 28/5/20 5:14 pm, Brendan Simon (eTRIX) wrote:
> Hi,
>
> Before I embark on my own implementation of a failsafe bootloading
> process from my embedded system (Xilinx Zynq board booting from SD
> Card), I thought I'd quickly ask the experts if there are any standard
> implementations in u-boot.
>
> The current u-boot being used is from 2015.  It probably needs to be
> updated (for various reasons).  It is loaded from the first partition
> (64MB/FAT32) of an SD Card as part of a file called `BOOT.BIN`.  The
> `Env.txt` file contains settings for two linux root systems (including
> kernel and dtb) on separate partitions (ext4/1GB).  The first
> statement in `Env.txt` has a `part=2` or `part=3` to indicate, which
> partition to boot from (load kernel and set cmdline for rootfs, etc).
>
> My simple approach was to store a env var for the number of reboot
> attempts.  On every boot attempt, the env var would be incremented. 
> If linux booted successfully it would set the env var to zero (I
> believe there are linux tools to do that).  If linux didn't boot
> successfully, eventually the reboot count env var would reach some
> value, where the alternative partition would be selected as an attempt
> to get something booting and up and running.
>
> NOTE: the devices are remote and need to be up as much as possible so
> they can be monitored/managed.
>
> *Does this type of functionality exist already in u-boot?*  I'm
> guessing/hoping it does (and hope to use it directly or leverage the
> features that make sense) rather than reinventing the wheel.
>
> *Where is the best place to go to get information/documentation on this?*
>
> Finally, I'm looking at migrating to EMMC, maybe with a golden image
> for failsafe use, and two partitions for current filesystem and
> next/upgrade filesystem.
>
> *Is there any documentation that might be a useful in this use case?*
>
> Thanks, Brendan.
>