Generic SPL framework
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=====================
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Overview
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--------
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To unify all existing implementations for a secondary program loader (SPL)
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and to allow simply adding of new implementations this generic SPL framework
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has been created. With this framework almost all source files for a board
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can be reused. No code duplication or symlinking is necessary anymore.
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How it works
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------------
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The object files for SPL are built separately and placed in the "spl" directory.
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The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
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u-boot-spl.map.
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A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL.
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Source files can therefore be compiled for SPL with different settings.
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For example:
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ifeq ($(CONFIG_SPL_BUILD),y)
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obj-y += board_spl.o
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else
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obj-y += board.o
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endif
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obj-$(CONFIG_SPL_BUILD) += foo.o
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#ifdef CONFIG_SPL_BUILD
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foo();
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#endif
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The building of SPL images can be enabled by CONFIG_SPL option in Kconfig.
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Because SPL images normally have a different text base, one has to be
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configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be
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defined with CONFIG_SPL_LDSCRIPT.
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To support generic U-Boot libraries and drivers in the SPL binary one can
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optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
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are supported:
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CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
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CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
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CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
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CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
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CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
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CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
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CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
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CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
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CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o)
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CONFIG_SPL_EXT_SUPPORT
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CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
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CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)
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CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/raw/libnand.o)
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CONFIG_SPL_DRIVERS_MISC_SUPPORT (drivers/misc)
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CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o)
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CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o)
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CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/raw/nand_spl_load.o)
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CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)
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CONFIG_SPL_RAM_DEVICE (common/spl/spl.c)
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CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o)
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Debugging
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---------
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When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG
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as in most cases do_reset is not defined within SPL.
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Estimating stack usage
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----------------------
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With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate
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stack usage at various points in run sequence of SPL. The -fstack-usage option
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to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that
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will give stack usage information and cflow can construct program flow.
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Must have gcc 4.6 or later, which supports -fstack-usage
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1) Build normally
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2) Perform the following shell command to generate a list of C files used in
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SPL:
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$ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list
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3) Execute cflow:
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$ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER
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cflow will spit out a number of warnings as it does not parse
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the config files and picks functions based on #ifdef. Parsing the '.i'
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files instead introduces another set of headaches. These warnings are
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not usually important to understanding the flow, however.
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