1Generic SPL framework
2=====================
3
4Overview
5--------
6
7To unify all existing implementations for a secondary program loader (SPL)
8and to allow simply adding of new implementations this generic SPL framework
9has been created. With this framework almost all source files for a board
10can be reused. No code duplication or symlinking is necessary anymore.
11
12
13How it works
14------------
15
16The object files for SPL are built separately and placed in the "spl" directory.
17The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
18u-boot-spl.map.
19
20A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL.
21Source files can therefore be compiled for SPL with different settings.
22
23For example:
24
25ifeq ($(CONFIG_SPL_BUILD),y)
26obj-y += board_spl.o
27else
28obj-y += board.o
29endif
30
31obj-$(CONFIG_SPL_BUILD) += foo.o
32
33#ifdef CONFIG_SPL_BUILD
34	foo();
35#endif
36
37
38The building of SPL images can be enabled by CONFIG_SPL option in Kconfig.
39
40Because SPL images normally have a different text base, one has to be
41configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be
42defined with CONFIG_SPL_LDSCRIPT.
43
44To support generic U-Boot libraries and drivers in the SPL binary one can
45optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
46are supported:
47
48CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
49CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
50CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
51CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
52CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
53CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
54CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)
55CONFIG_SPL_SPI_SUPPORT (drivers/spi/libspi.o)
56CONFIG_SPL_FS_FAT (fs/fat/libfat.o)
57CONFIG_SPL_FS_EXT4
58CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
59CONFIG_SPL_POWER_SUPPORT (drivers/power/libpower.o)
60CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/raw/libnand.o)
61CONFIG_SPL_DRIVERS_MISC_SUPPORT (drivers/misc)
62CONFIG_SPL_DMA (drivers/dma/libdma.o)
63CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o)
64CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/raw/nand_spl_load.o)
65CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o)
66CONFIG_SPL_RAM_DEVICE (common/spl/spl.c)
67CONFIG_SPL_WATCHDOG_SUPPORT (drivers/watchdog/libwatchdog.o)
68
69Device tree
70-----------
71The U-Boot device tree is filtered by the fdtgrep tools during the build
72process to generate a much smaller device tree used in SPL (spl/u-boot-spl.dtb)
73with:
74- the mandatory nodes (/alias, /chosen, /config)
75- the nodes with one pre-relocation property:
76  'u-boot,dm-pre-reloc' or 'u-boot,dm-spl'
77
78fdtgrep is also used to remove:
79- the properties defined in CONFIG_OF_SPL_REMOVE_PROPS
80- all the pre-relocation properties
81  ('u-boot,dm-pre-reloc', 'u-boot,dm-spl' and 'u-boot,dm-tpl')
82
83All the nodes remaining in the SPL devicetree are bound
84(see doc/driver-model/design.rst).
85
86Debugging
87---------
88
89When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG
90as in most cases do_reset is not defined within SPL.
91
92
93Estimating stack usage
94----------------------
95
96With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate
97stack usage at various points in run sequence of SPL.  The -fstack-usage option
98to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that
99will give stack usage information and cflow can construct program flow.
100
101Must have gcc 4.6 or later, which supports -fstack-usage
102
1031) Build normally
1042) Perform the following shell command to generate a list of C files used in
105SPL:
106$ find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list
1073) Execute cflow:
108$ cflow --main=board_init_r `cat used-spl.list` 2>&1 | $PAGER
109
110cflow will spit out a number of warnings as it does not parse
111the config files and picks functions based on #ifdef.  Parsing the '.i'
112files instead introduces another set of headaches.  These warnings are
113not usually important to understanding the flow, however.
114