topic Re: How to Load initramfs from SD Card (Single FAT32 Boot Partition) in i.MX Processors

How to Load initramfs from SD Card (Single FAT32 Boot Partition)

NXP_USER_05 — Wed, 10 Dec 2025 15:57:38 GMT

Hi,

I am working on i.MX8M Plus EVK board and would like to boot Linux using initramfs as the root filesystem, loaded directly from an SD card boot partition only(FAT32).

The SD card does not contain a separate root filesystem partition.

Current Setup

SD card contains only one FAT32 boot partition
Files present on the FAT32 partition:
- Image(U-boot+kernel)
- Device Tree Blob (.dtb)
- initramfs image

Questions

initramfs Generation
- What is the recommended method to generate an initramfs image?
- Should initramfs be built into the kernel or loaded as a separate image?
- How can initramfs be loaded from the SD card (FAT32 partition) using U-Boot?
U-Boot Environment Commands
- What are the U-Boot commands or environment variables needed to Load the kernel, device tree, and initramfs from SD.

Re: How to Load initramfs from SD Card (Single FAT32 Boot Partition)

Zhiming_Liu — Mon, 15 Dec 2025 06:40:11 GMT

Hi,

What is the recommended method to generate an initramfs image?

--> You can build it with bitbake core-image-minimal-initramfs in Yocto.

Should initramfs be built into the kernel or loaded as a separate image?

--> It depends on your needs.

How can initramfs be loaded from the SD card (FAT32 partition) using U-Boot?
-->Here is example:

# If mmc0 is your sd card. setenv bootargs console=ttymxc0,115200 root=/dev/ram rw fatload mmc 0:1 ${loadaddr} Image fatload mmc 0:1 ${fdt_addr} imx8mp-evk.dtb fatload mmc 0:1 ${ramdisk_addr} xxxx_initramfs.cpio.gz booti ${loadaddr} ${ramdisk_addr}:${filesize} ${fdt_addr}

You can refer board/beacon/imx8mn/imx8mn_beacon.env

boot_fdt=try bootdelay=2 bootscript=echo Running bootscript from mmc ...; source console=ttymxc1 fdt_addr=0x45000000 fdt_file=imx8mn-beacon-kit.dtb finduuid=part uuid mmc ${mmcdev}:2 uuid image=Image initrd_addr=0x46000000 loadbootscript=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script}; loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file} loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image} loadramdisk=load mmc ${mmcdev} ${ramdisk_addr} ${ramdiskimage} mmcargs=setenv bootargs console=${console},${baudrate} root=PARTUUID=${uuid} rootwait rw ${mtdparts} ${optargs} mmcautodetect=yes mmcboot=echo Booting from mmc ...; run finduuid; run mmcargs; if test ${boot_fdt} = yes || test ${boot_fdt} = try; then if run loadfdt; then booti ${loadaddr} - ${fdt_addr}; else echo WARN: Cannot load the DT; fi; else echo wait for boot; fi; mmcdev=1 mmcpart=1 netargs=setenv bootargs console=${console},${baudrate} root=/dev/nfs ip=dhcp nfsroot=${serverip}:${nfsroot},v3,tcp netboot=echo Booting from net ...; run netargs; if test ${ip_dyn} = yes; then setenv get_cmd dhcp; else setenv get_cmd tftp; fi; ${get_cmd} ${loadaddr} ${image}; if test ${boot_fdt} = yes || test ${boot_fdt} = try; then if ${get_cmd} ${fdt_addr} ${fdt_file}; then booti ${loadaddr} - ${fdt_addr}; else echo WARN: Cannot load the DT; fi; else booti; fi; ramargs=setenv bootargs console=${console},${baudrate} root=/dev/ram rw ${optargs} ramboot=echo Booting from RAMdisk...; run loadimage; run loadfdt; fdt addr $fdt_addr; run loadramdisk; run ramargs; booti ${loadaddr} ${ramdisk_addr} ${fdt_addr} ${optargs} ramdisk_addr=0x46000000 ramdiskimage=rootfs.cpio.uboot script=boot.scr

Best Regards,
Zhiming

Re: How to Load initramfs from SD Card (Single FAT32 Boot Partition)

NXP_USER_05 — Mon, 15 Dec 2025 16:24:46 GMT

Hi @Zhiming_Liu ,

As per your guidance, I followed the procedure you shared.
I am able to successfully load the kernel Image and DTB, but the initramfs (cpio.gz) root filesystem is not being loaded by the kernel.

Below are the exact U-Boot commands and behavior.

U-Boot Commands Used

u-boot=> setenv bootargs console=ttymxc1,115200 root=/dev/ram rw

u-boot=> fatload mmc 1:1 ${loadaddr} Image_copy.gz 13450466 bytes read in 282 ms (45.5 MiB/s)

u-boot=> fatload mmc 1:1 ${fdt_addr} imx8mp-evk.dtb 82784 bytes read in 4 ms (19.7 MiB/s)

u-boot=> fatload mmc 1:1 ${ramdisk_addr_r} core-image-minimal-initramfs-imx8mp-ddr4-evk.cpio.gz 12602736 bytes read in 264 ms (45.5 MiB/s)

u-boot=> booti ${loadaddr} ${ramdisk_addr_r}:${filesize} ${fdt_addr}

After executing the booti command, the kernel starts booting, but it does not mount or use the initramfs (cpio.gz) as root filesystem.

I have attached the full kernel boot log for reference.

Questions

What could be the possible reasons for the kernel not loading the initramfs (cpio.gz) even though it is correctly loaded into memory by U-Boot?
Are there any mandatory kernel configuration options required for initramfs support that I should verify?
Is the bootargs configuration correct for booting with initramfs on i.MX8M Plus, or are additional parameters required?