Fast Boot for i.MX 8QXP Using U-Boot Falcon Mode

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The purpose of this article is to show how to reduce the boot time on i.MX 8QXP using U-Boot Falcon Mode. The general technique is presented in the AN14093. This article was tested on LF-6.6.23-2.0.0 BSP.

How to do it

1. Follow the steps in the i.MX Yocto Project User's Guide and prepare your Yocto building environment. We will further assume that the BSP is in the ~/imx-yocto-bsp directory and the build directory is ~/imx-yocto-bsp/build.

2. Unpack the attached archive in ~/imx-yocto-bsp/sources. This should create the ~/imx-yocto-bsp/sources/meta-imx-fastboot directory. 

3. Add the meta-imx-fastboot layer to your build using the following command:

bitbake-layers add-layer ~/imx-yocto-bsp/sources/meta-imx-fastboot

4. If you've previously built an image in the same tree, clean the u-boot-imx and imx-boot packages using the following command:

bitbake -c clean u-boot-imx imx-boot

5. Build the new image. Out of the box, this package is configured for core-image-minimal. We will show you below how to adapt it for other images:

bitbake core-image-minimal

6. Write the resulted image on eMMC/SD using your preferred method and boot the board.

7. By default, the board will boot normally. To enable fast boot, stop the board in U-Boot, and run the following command:

u-boot => run prepare_fdt

8. Reboot the board. From this point on, the board should boot in fast mode. Far less messages will be printed by the kernel or systemd during boot. You may further optimize the boot time by removing unnecessary features from the kernel and/or removing unnecessary services started by systemd. Please refer to AN14093.

9. If you ever want to re-enter U-Boot, please keep the 'c' key pressed in the serial console during board power-on. It's easiest if you press and keep the 'c' key pressed before powering on/pressing the reset button.

How it works

The layer we've added contains patches for U-Boot, ATF and imx-mkimage. In addition, it modifies the core-image-minimal recipe.

In U-Boot, the necessary options for Falcon Mode are added in a new configuration file, named imx8qxp_mek_falcon_defconfig, as well as an implementation of the spl_start_uboot() function.

In ATF, the device tree load address is added in the correct parameter.

In mkimage, two new targets are created: kernel-atf-container.img (to be deployed in the boot partition) and uImage (to be deployed in the rootfs).

The change in the core-image-minimal recipe ensures that the new files are copied in the resulting image.

If you want to build a different image, you need to copy the content of core-image-minimal.bbappend in a new file, named according to the image you want to build. For example, if you want to build imx-image-full, you could use the following command:

cp ~/imx-yocto-bsp/sources/meta-imx-fastboot/recipes-fsl/images/core-image-minimal.bbappend ~/imx-yocto-bsp/sources/meta-imx-fastboot/recipes-fsl/images/imx-image-full.bbappend

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