Multiple kernels and boot partitions selection

[Quentin Schulz]

Hi Gianluca,

On 10/10/22 09:06, gianluca wrote:
> Hello,
> I was wondering if there is/are some standard way(s) to achieve a 
> multiple boot selection on u-boot startup.
> 
> Let's say I have a bunch of partitions:
> 
> 1- /dev/mmcblk0p7 with Debian 11 Bullseye
> 
> 2- /dev/mmcblk0p5 with Debian 10 Buster
> 
> All of these partitions have the /boot/uImage kernel images, the 
> /lib/modules/$(uname -r) drivers folders and /boot/dtb device-trees into 
> their partition section.
> 
> u-boot has NOT the specific environment partition, i.e. it is located in 
> the end of bootloader itself up to the maximum size of the bootloader 
> partition. So, to be clear the /dev/mmcblk0p1 contains u-boot code & 
> envar space.
> 
> If needed I can have a MB85RC64 a 24LC64 FRAM/EEPROM compatible memory 
> chip to store information on boot.
> 

You can modify the U-Boot environment from userspace with fw_setenv from 
libubootenv (formerly u-boot(-fw)-tools). You can store from there which 
partition to use for the next boot in an environment variable.

Cheers,
Quentin