| Daniel Schwierzeck | 6a11cf4 | 2011-07-18 07:48:07 +0000 | [diff] [blame] | 1 | Generic SPL framework |
| 2 | ===================== |
| 3 | |
| 4 | Overview |
| 5 | -------- |
| 6 | |
| 7 | To unify all existing implementations for a secondary program loader (SPL) |
| 8 | and to allow simply adding of new implementations this generic SPL framework |
| 9 | has been created. With this framework almost all source files for a board |
| 10 | can be reused. No code duplication or symlinking is necessary anymore. |
| 11 | |
| 12 | |
| 13 | How it works |
| 14 | ------------ |
| 15 | |
| 16 | There is a new directory TOPDIR/spl which contains only a Makefile. |
| 17 | The object files are built separately for SPL and placed in this directory. |
| 18 | The final binaries which are generated are u-boot-spl, u-boot-spl.bin and |
| 19 | u-boot-spl.map. |
| 20 | |
| 21 | During the SPL build a variable named CONFIG_SPL_BUILD is exported |
| 22 | in the make environment and also appended to CPPFLAGS with -DCONFIG_SPL_BUILD. |
| 23 | Source files can therefore be compiled for SPL with different settings. |
| 24 | ARM-based boards have previously used the option CONFIG_PRELOADER for it. |
| 25 | |
| 26 | For example: |
| 27 | |
| 28 | ifeq ($(CONFIG_SPL_BUILD),y) |
| 29 | COBJS-y += board_spl.o |
| 30 | else |
| 31 | COBJS-y += board.o |
| 32 | endif |
| 33 | |
| 34 | COBJS-$(CONFIG_SPL_BUILD) += foo.o |
| 35 | |
| 36 | #ifdef CONFIG_SPL_BUILD |
| 37 | foo(); |
| 38 | #endif |
| 39 | |
| 40 | |
| 41 | The building of SPL images can be with: |
| 42 | |
| 43 | #define CONFIG_SPL |
| 44 | |
| 45 | Because SPL images normally have a different text base, one have to be |
| 46 | configured by defining CONFIG_SPL_TEXT_BASE. The linker script have to be |
| 47 | defined with CONFIG_SPL_LDSCRIPT. |
| 48 | |
| 49 | To support generic U-Boot libraries and drivers in the SPL binary one can |
| 50 | optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options |
| 51 | are supported: |
| 52 | |
| 53 | CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o) |
| 54 | CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o) |
| 55 | CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o) |
| 56 | CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o) |
| 57 | CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o) |
| 58 | CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o) |
| 59 | CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o) |
| 60 | CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o) |
| 61 | CONFIG_SPL_FAT_SUPPORT (fs/fat/libfat.o) |
| 62 | CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o) |