Re: [RAUC] boot-mbr-switch from u-boot

[Michael Tretter <m.tretter@pengutronix.de>]

Hello Martin,

On Thu, 26 Nov 2020 08:57:49 +0000, Martin Hollingsworth wrote:
> I am integrating RAUC into a Xilinx ZynqMP device and using boot-mbr-switch
> method according to documentation chapter 7.6.2. Bootloader is u-boot, RAUC
> u-boot scripts are from contrib/uboot.sh, RAUC is v1.2 (upgrade planned).
> 
> When switching between slots from within u-boot the MBR partition table is
> not altered. So when installing a new system (inclduing new bootloader
> partition content) which doesn't boot 3 times, after the fallback we run the
> new bootloader partition with the old rootfs. Do I understand this from the
> source code correctly?

Correct.

> 
> In my opinion this is a major problem, because on Xilinx ZynqMP the
> bootloader partition contains the Xilinx bootbin, a first stage bootloader
> which flashes the FPGA firmware before starting u-boot. In this case we run
> the old linux against a new FPGA and have an inconsistent system after the
> RAUC fallback.

How do you tell Linux, what is contained in the FPGA firmware? Linux should
not make any assumptions about the loaded FPGA firmware.

> 
> Does anyone have a solution for this problem?

There are a few solutions:

You could use a different mechanism to load the firmware. Instead of the
boot.bin, put the bitstream into the rootfs (or another partition) and load it
from the bootloader (I'm not sure, if U-Boot supports this, but Barebox does.)
or from Linux.

If it is mandatory to load the firmware from the FSBL (or the bootloader
partition in general), you would need a means to tell Linux, which firmware
was loaded. That information has to be stored in the updated bootloader
partition.

Michael

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