1Generic SPL framework 2===================== 3 4Overview 5-------- 6 7To unify all existing implementations for a secondary program loader (SPL) 8and to allow simply adding of new implementations this generic SPL framework 9has been created. With this framework almost all source files for a board 10can be reused. No code duplication or symlinking is necessary anymore. 11 12 13How it works 14------------ 15 16The object files for SPL are built separately and placed in the "spl" directory. 17The final binaries which are generated are u-boot-spl, u-boot-spl.bin and 18u-boot-spl.map. 19 20A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL. 21Source files can therefore be compiled for SPL with different settings. 22 23For example: 24 25ifeq ($(CONFIG_SPL_BUILD),y) 26obj-y += board_spl.o 27else 28obj-y += board.o 29endif 30 31obj-$(CONFIG_SPL_BUILD) += foo.o 32 33#ifdef CONFIG_SPL_BUILD 34 foo(); 35#endif 36 37 38The building of SPL images can be enabled by CONFIG_SPL option in Kconfig. 39 40Because SPL images normally have a different text base, one has to be 41configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be 42defined with CONFIG_SPL_LDSCRIPT. 43 44To support generic U-Boot libraries and drivers in the SPL binary one can 45optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options 46are supported: 47 48CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o) 49CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o) 50CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o) 51CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o) 52CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o) 53CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o) 54CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o) 55CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o) 56CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o) 57CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o) 58CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o) 59CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o) 60CONFIG_SPL_DRIVERS_MISC_SUPPORT (drivers/misc) 61CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o) 62CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o) 63CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/nand_spl_load.o) 64CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o) 65CONFIG_SPL_RAM_DEVICE (common/spl/spl.c) 66CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o) 67 68 69Debugging 70--------- 71 72When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG 73as in most cases do_reset is not defined within SPL. 74 75 76Estimating stack usage 77---------------------- 78 79With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate 80stack usage at various points in run sequence of SPL. The -fstack-usage option 81to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that 82will give stack usage information and cflow can construct program flow. 83 84Must have gcc 4.6 or later, which supports -fstack-usage 85 861) Build normally 872) Perform the following shell command to generate a list of C files used in 88SPL: 89$ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list 903) Execute cflow: 91$ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER 92 93cflow will spit out a number of warnings as it does not parse 94the config files and picks functions based on #ifdef. Parsing the '.i' 95files instead introduces another set of headaches. These warnings are 96not usually important to understanding the flow, however. 97