README.SPL 3.8 KB

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  1. Generic SPL framework
  2. =====================
  3. Overview
  4. --------
  5. To unify all existing implementations for a secondary program loader (SPL)
  6. and to allow simply adding of new implementations this generic SPL framework
  7. has been created. With this framework almost all source files for a board
  8. can be reused. No code duplication or symlinking is necessary anymore.
  9. How it works
  10. ------------
  11. The object files for SPL are built separately and placed in the "spl" directory.
  12. The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
  13. u-boot-spl.map.
  14. A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL.
  15. Source files can therefore be compiled for SPL with different settings.
  16. For example:
  17. ifeq ($(CONFIG_SPL_BUILD),y)
  18. obj-y += board_spl.o
  19. else
  20. obj-y += board.o
  21. endif
  22. obj-$(CONFIG_SPL_BUILD) += foo.o
  23. #ifdef CONFIG_SPL_BUILD
  24. foo();
  25. #endif
  26. The building of SPL images can be enabled by CONFIG_SPL option in Kconfig.
  27. Because SPL images normally have a different text base, one has to be
  28. configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be
  29. defined with CONFIG_SPL_LDSCRIPT.
  30. To support generic U-Boot libraries and drivers in the SPL binary one can
  31. optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
  32. are supported:
  33. CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
  34. CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
  35. CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
  36. CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
  37. CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
  38. CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
  39. CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
  40. CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
  41. CONFIG_SPL_FS_FAT (fs/fat/libfat.o)
  42. CONFIG_SPL_FS_EXT4
  43. CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
  44. CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)
  45. CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/raw/libnand.o)
  46. CONFIG_SPL_DRIVERS_MISC_SUPPORT (drivers/misc)
  47. CONFIG_SPL_DMA_SUPPORT (drivers/dma/libdma.o)
  48. CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o)
  49. CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/raw/nand_spl_load.o)
  50. CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)
  51. CONFIG_SPL_RAM_DEVICE (common/spl/spl.c)
  52. CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o)
  53. Device tree
  54. -----------
  55. The U-Boot device tree is filtered by the fdtgrep tools during the build
  56. process to generate a much smaller device tree used in SPL (spl/u-boot-spl.dtb)
  57. with:
  58. - the mandatory nodes (/alias, /chosen, /config)
  59. - the nodes with one pre-relocation property:
  60. 'u-boot,dm-pre-reloc' or 'u-boot,dm-spl'
  61. fdtgrep is also used to remove:
  62. - the properties defined in CONFIG_OF_SPL_REMOVE_PROPS
  63. - all the pre-relocation properties
  64. ('u-boot,dm-pre-reloc', 'u-boot,dm-spl' and 'u-boot,dm-tpl')
  65. All the nodes remaining in the SPL devicetree are bound
  66. (see driver-model/README.txt).
  67. Debugging
  68. ---------
  69. When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG
  70. as in most cases do_reset is not defined within SPL.
  71. Estimating stack usage
  72. ----------------------
  73. With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate
  74. stack usage at various points in run sequence of SPL. The -fstack-usage option
  75. to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that
  76. will give stack usage information and cflow can construct program flow.
  77. Must have gcc 4.6 or later, which supports -fstack-usage
  78. 1) Build normally
  79. 2) Perform the following shell command to generate a list of C files used in
  80. SPL:
  81. $ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list
  82. 3) Execute cflow:
  83. $ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER
  84. cflow will spit out a number of warnings as it does not parse
  85. the config files and picks functions based on #ifdef. Parsing the '.i'
  86. files instead introduces another set of headaches. These warnings are
  87. not usually important to understanding the flow, however.