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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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There is a new directory TOPDIR/spl which contains only a Makefile.
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The object files are built separately for SPL and placed in this 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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During the SPL build a variable named CONFIG_SPL_BUILD is exported
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in the make environment and also appended to CPPFLAGS with -DCONFIG_SPL_BUILD.
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Source files can therefore be compiled for SPL with different settings.
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ARM-based boards have previously used the option CONFIG_PRELOADER for it.
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For example:
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ifeq ($(CONFIG_SPL_BUILD),y)
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COBJS-y += board_spl.o
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else
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COBJS-y += board.o
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endif
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COBJS-$(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 with:
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#define CONFIG_SPL
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Because SPL images normally have a different text base, one have to be
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configured by defining CONFIG_SPL_TEXT_BASE. The linker script have 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_LIBGENERIC_SUPPORT (lib/libgeneric.o)
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