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Add details regarding scheme which need to be followed in SPL and further stages for those regions which need to be preserved across bootstages. Signed-off-by: Devarsh Thakkar <devarsht@ti.com> Reviewed-by: Simon Glass <sjg@chromium>
204 lines
7.1 KiB
ReStructuredText
204 lines
7.1 KiB
ReStructuredText
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 (drivers/i2c/libi2c.o)
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CONFIG_SPL_GPIO (drivers/gpio/libgpio.o)
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CONFIG_SPL_MMC (drivers/mmc/libmmc.o)
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CONFIG_SPL_SERIAL (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 (drivers/spi/libspi.o)
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CONFIG_SPL_FS_FAT (fs/fat/libfat.o)
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CONFIG_SPL_FS_EXT4
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CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o)
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CONFIG_SPL_POWER (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 (drivers/misc)
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CONFIG_SPL_DMA (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 (drivers/watchdog/libwatchdog.o)
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CONFIG_SPL_SYSCON (drivers/core/syscon-uclass.o)
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CONFIG_SPL_GZIP (lib/gzip.o)
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CONFIG_SPL_VIDEO (drivers/video/video-uclass.o drivers/video/vidconsole-uclass.o)
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CONFIG_SPL_SPLASH_SCREEN (common/splash.o)
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CONFIG_SPL_SPLASH_SOURCE (common/splash_source.o)
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CONFIG_SPL_GPIO (drivers/gpio)
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CONFIG_SPL_DM_GPIO (drivers/gpio/gpio-uclass.o)
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CONFIG_SPL_BMP (drivers/video/bmp.o)
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CONFIG_SPL_BLOBLIST (common/bloblist.o)
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Adding SPL-specific code
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------------------------
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To check whether a feature is enabled, use CONFIG_IS_ENABLED()::
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if (CONFIG_IS_ENABLED(CLK))
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...
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This checks CONFIG_CLK for the main build, CONFIG_SPL_CLK for the SPL build,
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CONFIG_TPL_CLK for the TPL build, etc.
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U-Boot Boot Phases
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------------------
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U-Boot goes through the following boot phases where TPL, VPL, SPL are optional.
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While many boards use SPL, less use TPL.
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TPL
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Very early init, as tiny as possible. This loads SPL (or VPL if enabled).
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VPL
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Optional verification step, which can select one of several SPL binaries,
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if A/B verified boot is enabled. Implementation of the VPL logic is
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work-in-progress. For now it just boots into SPL.
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SPL
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Secondary program loader. Sets up SDRAM and loads U-Boot proper. It may also
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load other firmware components.
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U-Boot
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U-Boot proper, containing the command line and boot logic.
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Further usages of U-Boot SPL comprise:
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* Launching BL31 of ARM Trusted Firmware which invokes main U-Boot as BL33
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* launching EDK II
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* launching Linux kernel
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* launching RISC-V OpenSBI which invokes main U-Boot
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Checking the boot phase
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-----------------------
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Use `spl_phase()` to find the current U-Boot phase, e.g. `PHASE_SPL`. You can
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also find the previous and next phase and get the phase name.
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Device tree
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-----------
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The U-Boot device tree is filtered by the fdtgrep tools during the build
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process to generate a much smaller device tree used in SPL (spl/u-boot-spl.dtb)
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with:
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- the mandatory nodes (/alias, /chosen, /config)
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- the nodes with one pre-relocation property:
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'bootph-all' or 'bootph-pre-ram'
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fdtgrep is also used to remove:
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- the properties defined in CONFIG_OF_SPL_REMOVE_PROPS
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- all the pre-relocation properties
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('bootph-all', 'bootph-pre-ram' (SPL), 'bootph-pre-sram' (TPL) and
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'bootph-verify' (TPL))
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All the nodes remaining in the SPL devicetree are bound
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(see doc/driver-model/design.rst).
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NOTE: U-Boot migrated to a new schema for the u-boot,dm-* tags in 2023. Please
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update to use the new bootph-* tags as described in the
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doc/device-tree-bindings/bootph.yaml binding file.
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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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#. Build normally
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#. 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$:.c:' > used-spl.list`
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#. Execute cflow:
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`$ 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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Reserving memory in SPL
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-----------------------
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If memory needs to be reserved in RAM during SPL stage with the requirement that
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the SPL reserved memory remains preserved across further boot stages too
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then it needs to be reserved mandatorily starting from end of RAM. This is to
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ensure that further stages can simply skip this region before carrying out
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further reservations or updating the relocation address.
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Also out of these regions which are to be preserved across further stages of
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boot, video framebuffer memory region must be reserved first starting from
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end of RAM for which helper function spl_reserve_video_from_ram_top is provided
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which makes sure that video memory is placed at top of reservation area with
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further reservations below it.
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The corresponding information of reservation for those regions can be passed to
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further boot stages using a bloblist. For e.g. the information for
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framebuffer area reserved by SPL can be passed onto U-boot using
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BLOBLISTT_U_BOOT_VIDEO.
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The further boot stages need to parse each of the bloblist passed from SPL stage
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starting from video bloblist and skip this whole SPL reserved memory area from
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end of RAM as per the bloblists received, before carrying out further
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reservations or updating the relocation address. For e.g, U-boot proper uses
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function "setup_relocaddr_from_bloblist" to parse the bloblists passed from
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previous stage and skip the memory reserved from previous stage accordingly.
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