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 16There is a new directory TOPDIR/spl which contains only a Makefile. 17The object files are built separately for SPL and placed in this directory. 18The final binaries which are generated are u-boot-spl, u-boot-spl.bin and 19u-boot-spl.map. 20 21During the SPL build a variable named CONFIG_SPL_BUILD is exported 22in the make environment and also appended to CPPFLAGS with -DCONFIG_SPL_BUILD. 23Source files can therefore be compiled for SPL with different settings. 24ARM-based boards have previously used the option CONFIG_PRELOADER for it. 25 26For example: 27 28ifeq ($(CONFIG_SPL_BUILD),y) 29COBJS-y += board_spl.o 30else 31COBJS-y += board.o 32endif 33 34COBJS-$(CONFIG_SPL_BUILD) += foo.o 35 36#ifdef CONFIG_SPL_BUILD 37 foo(); 38#endif 39 40 41The building of SPL images can be with: 42 43#define CONFIG_SPL 44 45Because SPL images normally have a different text base, one has to be 46configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be 47defined with CONFIG_SPL_LDSCRIPT. 48 49To support generic U-Boot libraries and drivers in the SPL binary one can 50optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options 51are supported: 52 53CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o) 54CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o) 55CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o) 56CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o) 57CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o) 58CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o) 59CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o) 60CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o) 61CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o) 62CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o) 63CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o) 64CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/libnand.o) 65CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o) 66CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o) 67CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/nand_spl_load.o) 68CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o) 69 70 71Normally CPU is assumed to be the same between the SPL and normal 72u-boot build. However it is possible to specify a different CPU for 73the SPL build for cases where the SPL is expected to run on a 74different CPU model from the main u-boot. This is done by specifying 75an SPL CPU in boards.cfg as follows: 76 77 normal_cpu:spl_cpu 78 79This this case CPU will be set to "normal_cpu" during the main u-boot 80build and "spl_cpu" during the SPL build. 81 82 83Debugging 84--------- 85 86When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG 87as in most cases do_reset is not defined within SPL. 88 89 90Estimating stack usage 91---------------------- 92 93With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate 94stack usage at various points in run sequence of SPL. The -fstack-usage option 95to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that 96will give stack usage information and cflow can construct program flow. 97 98Must have gcc 4.6 or later, which supports -fstack-usage 99 1001) Build normally 1012) Perform the following shell command to generate a list of C files used in 102SPL: 103$ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list 1043) Execute cflow: 105$ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER 106 107cflow will spit out a number of warnings as it does not parse 108the config files and picks functions based on #ifdef. Parsing the '.i' 109files instead introduces another set of headaches. These warnings are 110not usually important to understanding the flow, however. 111