An example of a minimal kernel configuration for a Wandboard that is able to boot from a microSD card root filesystem is the arch/arm/configs/wandboard-custom-minimal_defconfig file:
CONFIG_KERNEL_XZ=y # CONFIG_SWAP is not set CONFIG_NO_HZ=y CONFIG_HIGH_RES_TIMERS=y CONFIG_CC_OPTIMIZE_FOR_SIZE=y # CONFIG_KALLSYMS is not set # CONFIG_PRINTK is not set # CONFIG_BUG is not set # CONFIG_ELF_CORE is not set # CONFIG_BASE_FULL is not set CONFIG_EMBEDDED=y CONFIG_SLOB=y CONFIG_ARCH_MXC=y CONFIG_SOC_IMX6Q=y # CONFIG_SWP_EMULATE is not set CONFIG_ARM_ERRATA_814220=y CONFIG_SMP=y CONFIG_VMSPLIT_2G=y CONFIG_AEABI=y CONFIG_CPU_FREQ=y # CONFIG_CPU_FREQ_STAT is not set CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y CONFIG_ARM_IMX6Q_CPUFREQ=y CONFIG_CPU_IDLE=y CONFIG_VFP=y CONFIG_NEON=y CONFIG_DEVTMPFS=y CONFIG_DEVTMPFS_MOUNT=y # CONFIG_INPUT_MOUSEDEV is not set # CONFIG_INPUT_KEYBOARD is not set # CONFIG_INPUT_MOUSE is not set CONFIG_SERIAL_IMX=y CONFIG_SERIAL_IMX_CONSOLE=y # CONFIG_HWMON is not set CONFIG_REGULATOR=y CONFIG_REGULATOR_ANATOP=y # CONFIG_USB_SUPPORT is not set CONFIG_MMC=y CONFIG_MMC_SDHCI=y CONFIG_MMC_SDHCI_PLTFM=y CONFIG_MMC_SDHCI_ESDHC_IMX=y CONFIG_DMADEVICES=y CONFIG_IMX_SDMA=y CONFIG_EXT3_FS=y # CONFIG_EXT3_FS_XATTR is not set CONFIG_EXT4_FS=y # CONFIG_PROC_SYSCTL is not set # CONFIG_PROC_PAGE_MONITOR is not set # CONFIG_SYSFS is not set # CONFIG_ENABLE_WARN_DEPRECATED is not set # CONFIG_ENABLE_MUST_CHECK is not set # CONFIG_FTRACE is not set # CONFIG_ARM_UNWIND is not set
This configuration builds an 867K compressed Linux kernel image (zImage) for a 3.4 MB vmlinux ELF image.