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- 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_SUPPORT (drivers/i2c/libi2c.o)
- CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
- CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
- CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
- CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
- CONFIG_SPL_SPI_SUPPORT (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_SUPPORT (drivers/power/libpower.o)
- CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/raw/libnand.o)
- CONFIG_SPL_DRIVERS_MISC_SUPPORT (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_SUPPORT (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.
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