Write swap_info fails due to HW ECC

[kebadopp]

Hello community,

I have ported mcuboot to STM32G4 platform. Here the internal flash has an underlying HW ECC - so when a flash dword is written with 0xFF data once it can't be re-written anymore until the entire page is deleted.

When updating an image (using mode MCUBOOT_SWAP_USING_SCRATCH) by swapping from secondary area to primary area the trailer data on primary area is not erased.
Therefore when at the end of the update process the function boot_write_swap_size is called on fap_primary_slot, the write call fails due to multiple write to flash dword.

If I flash the initial firmware in HEX format which skips initial writing 0xFF dwords it works like charm.

So I'm wondering what is the correct approach on this situation?
Should it be handled in the port specific implementation of flash_area_write / flash_area_erased_val / ...?
Or is it guaranteed mcuboot only write once to these dwords and so if they are not written during initial flashing everything is ok?

I found issues / pull requests addressing this topic like

• Multiple SoCs have flash configurations unsupported by MCUboot Multiple SoCs have flash configurations unsupported by MCUboot #713 (Multiple SoCs have flash configurations unsupported by MCUboot #713)
• imgtool: erased values should be omitted in trailer imgtool: erased values should be omitted in trailer #1288 (imgtool: erased values should be omitted in trailer #1288)