dd is writing my image wrong resulting in kernel panic

Question

I'm using dd to flash my buildroot image to an eMMC of my SBC. eMMC is connected as mass storage. The image is created with genimage and have some 'holes' in it.

genimage.cfg

image sdcard.img {
    hdimage {
    }

    partition u-boot {
        bootable = true
        image = "u-boot.bin"
        size = 2M
        in-partition-table = false
        offset = 0
        holes = {"(440; 512)"}
    }
    
    partition rootfsA {
        partition-type = 0x83
        image = "rootfs.ext2"
        offset = 3M
    }

    partition data {
        partition-type = 0x83
        image = "data.ext2"
    }
}

image data.ext2 {
    name = "data"
    ext4 {
        label = "data"
    }
    srcpath = "/home/<user>/buildroot_radxa/buildroot-2022.11/my_files/data_partition"
    size = 32MB
}

• the writing speed is much lower that the max writing speed (around 5MB/s out of 20MB/s)
• after dd finished I have a corrupt filesystem resulting kernel panic
• after trying a second time, the process is finished in second with GB/s speed
• on rare occasions it works as expected

dd command

sudo dd if=$img_path of=/dev/sdd status=progress bs=1024 conv=fsync

On the other hand I can flash the image with balenaEtcher and the system if fully operational.

What am I missing here?

Answer 1

As it turns out the device has its own physical partitions on the eMMC. So to avoid the error I described, I need to clean the eMMC with U-Boot binaries provided by the manufacturer. Official doc

sudo boot-g12.py radxa-zero-erase-emmc.bin 

Now I can use dd in a script.

Strange is still the write speed with balenaEtecher is higher (ca. 10MB/s) compared to dd (ca. 5MB/s). Already changed device. Tried bs=2048 and bs=4096.