Confusion about i.MX8MM Redundant Boot

[Sampo]

I am attempting to use Redundant Boot to implement robust bootloader update. And I have partly succeeded, but I have witnessed some confusing behavior.

We are using i.MX8MM with eMMC. The eMMC has two boot partitions. We are using U-Boot compiled with Yocto from the uboot-imx Github repository.

I am successfully able to create the Secondary Image Table on partition boot0. If the bootloader at address 0x42 does not work, the secondary bootloader at address 0x1000 + 0x42 is loaded just as intended.

But now for the confusion: If boot1 does not contain a valid bootloader, the device will not boot. U-Boot gives the following error:

mmc_load_image_raw_sector: mmc block read error
SPL: failed to boot from all boot devices
### ERROR ### Please RESET the board ###

If boot0 at address 0x42 contains a valid bootloader, the device boots, regardless of what boot1 contains.

I did a bit of debugging, and SPL is attempting to read from boot1 when PERSIST_SECONDARY_BOOT is 1 but the bootloader is on boot0. This the code that causes this is in uboot-imx/arch/arm/mach-imx/imx8m/soc.c:

/*
* Swap the eMMC boot partitions in case there was a
* fallback event (i.e. primary image was corrupted
* and that corruption was recognized by the BootROM),
* so the SPL loads the rest of the U-Boot from the
* correct eMMC boot partition, since the BootROM
* leaves the boot partition set to the corrupted one.
*/
if (part == 1)
part = 2;
else if (part == 2)
part = 1;
continue;

I initially thought this was a bug in U-Boot, and I commented out the code. But this caused secondary boot to fail altogether, where before it worked. As far as I understood it, secondary boot happens inside one eMMC boot partition, and the contents of the other partition should not effect the boot. But clearly it does.

Am I understanding something wrong, or is there a bug in U-Boot?

[Rita_Wang]

Which version BSP are you using? How do you download images to the emmc?Using the uuu tool?

[Sampo]

I am using target imx8mm_evk with Yocto kirkstone release (version 4.0.4).

I update the bootloader with dd as instructed here: https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/i-MX-8MQ-ROM-Redundant-Boot-for-expansio...

Following those instructions, I can successfully get the device to start from boot0 secondary bootloader.  I have verified from both the eMMC registers and PERSIST_SECONDARY_BOOT that this is the case. But if I for example use dd to write boot1 full of zeroes, the device does not boot anymore. And I don't understand why, boot1 should not affect starting of the device in any way.

[Rita_Wang]

For the Redundant Boot procedure :

1. Program primary image to boot0 and secondary image to boot1.
2. In u-boot, set boot partition with partconf command.

  Then in boot, when one image boot failed, e.g., image in boot0, ROM will try to boot from boot1.

[hustdage]

The following link shows, the redunant boot is in the same partition  using tag to know the offset.

It could not swtich dfferent boot partiton.

https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/i-MX-8MQ-ROM-Redundant-Boot-for-expansio...

Also, I found this link is the same as above using tag.

https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/i-MX8MM-SDCARD-Secondary-Boot-Demo/ta-p/...

What you said I believe is i.MX8XP, which can switch between boot1 and boot2.

https://community.nxp.com/t5/i-MX-Community-Articles/i-MX8QXP-eMMC-Secondary-Boot/ba-p/1257704#M45