Generic SPL framework ===================== Overview -------- To unify all existing implementations for a secondary program loader (SPL) and to allow simply adding of new implementations this generic SPL framework has been created. With this framework almost all source files for a board can be reused. No code duplication or symlinking is necessary anymore. How it works ------------ The object files for SPL are built separately and placed in the "spl" directory. The final binaries which are generated are u-boot-spl, u-boot-spl.bin and u-boot-spl.map. A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL. Source files can therefore be compiled for SPL with different settings. For example: ifeq ($(CONFIG_SPL_BUILD),y) obj-y += board_spl.o else obj-y += board.o endif obj-$(CONFIG_SPL_BUILD) += foo.o #ifdef CONFIG_SPL_BUILD foo(); #endif The building of SPL images can be enabled by CONFIG_SPL option in Kconfig. Because SPL images normally have a different text base, one has to be configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be defined with CONFIG_SPL_LDSCRIPT. To support generic U-Boot libraries and drivers in the SPL binary one can optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options are supported: CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o) CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o) CONFIG_SPL_I2C (drivers/i2c/libi2c.o) CONFIG_SPL_GPIO (drivers/gpio/libgpio.o) CONFIG_SPL_MMC (drivers/mmc/libmmc.o) CONFIG_SPL_SERIAL (drivers/serial/libserial.o) CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o) CONFIG_SPL_SPI (drivers/spi/libspi.o) CONFIG_SPL_FS_FAT (fs/fat/libfat.o) CONFIG_SPL_FS_EXT4 CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o) CONFIG_SPL_POWER (drivers/power/libpower.o) CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/raw/libnand.o) CONFIG_SPL_DRIVERS_MISC (drivers/misc) CONFIG_SPL_DMA (drivers/dma/libdma.o) CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o) CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/raw/nand_spl_load.o) CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o) CONFIG_SPL_RAM_DEVICE (common/spl/spl.c) CONFIG_SPL_WATCHDOG (drivers/watchdog/libwatchdog.o) Device tree ----------- The U-Boot device tree is filtered by the fdtgrep tools during the build process to generate a much smaller device tree used in SPL (spl/u-boot-spl.dtb) with: - the mandatory nodes (/alias, /chosen, /config) - the nodes with one pre-relocation property: 'u-boot,dm-pre-reloc' or 'u-boot,dm-spl' fdtgrep is also used to remove: - the properties defined in CONFIG_OF_SPL_REMOVE_PROPS - all the pre-relocation properties ('u-boot,dm-pre-reloc', 'u-boot,dm-spl' and 'u-boot,dm-tpl') All the nodes remaining in the SPL devicetree are bound (see doc/driver-model/design.rst). Debugging --------- When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG as in most cases do_reset is not defined within SPL. Estimating stack usage ---------------------- With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate stack usage at various points in run sequence of SPL. The -fstack-usage option to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that will give stack usage information and cflow can construct program flow. Must have gcc 4.6 or later, which supports -fstack-usage 1) Build normally 2) Perform the following shell command to generate a list of C files used in SPL: $ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list 3) Execute cflow: $ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER cflow will spit out a number of warnings as it does not parse the config files and picks functions based on #ifdef. Parsing the '.i' files instead introduces another set of headaches. These warnings are not usually important to understanding the flow, however.