| Generic xPL framework |
| ===================== |
| |
| Overview |
| -------- |
| |
| To unify all existing implementations for secondary/tertiary program loaders |
| (generically called xPL) |
| and to allow simply adding of new implementations this generic xPL framework |
| has been created. With this framework almost all source files for a board |
| can be reused. No code duplication or symlinking is necessary anymore. |
| |
| |
| How it works |
| ------------ |
| |
| The object files for xPL are built separately and placed in a subdirectory |
| ("spl", "tpl" or "vpl"). |
| The final binaries which are generated for SPL are u-boot-spl, u-boot-spl.bin |
| and u-boot-spl.map |
| |
| A config option named CONFIG_XPL_BUILD is enabled by Kconfig for xPL builds. |
| Source files can therefore be compiled for xPL with different settings. |
| |
| For example:: |
| |
| ifeq ($(CONFIG_XPL_BUILD),y) |
| obj-y += board_spl.o |
| else |
| obj-y += board.o |
| endif |
| |
| obj-$(CONFIG_XPL_BUILD) += foo.o |
| |
| if (IS_ENABLED(CONFIG_XPL_BUILD)) |
| foo(); |
| |
| if (xpl_phase() == PHASE_TPL) |
| bar(); |
| |
| The building of xPL images can be enabled by CONFIG_SPL (etc.) options in |
| Kconfig. |
| |
| Because xPL images normally have a different text base, one has to be |
| configured by defining CONFIG_xPL_TEXT_BASE. The linker script has to be |
| defined with CONFIG_xPL_LDSCRIPT. |
| |
| To support generic U-Boot libraries and drivers in the xPL binary one can |
| optionally define CONFIG_xPL_XXX_SUPPORT. Currently following options |
| are supported: |
| |
| CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o) |
| CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o) |
| CONFIG_SPL_I2C (drivers/i2c/libi2c.o) |
| CONFIG_SPL_GPIO (drivers/gpio/libgpio.o) |
| CONFIG_SPL_MMC (drivers/mmc/libmmc.o) |
| CONFIG_SPL_SERIAL (drivers/serial/libserial.o) |
| CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o) |
| CONFIG_SPL_SPI (drivers/spi/libspi.o) |
| CONFIG_SPL_FS_FAT (fs/fat/libfat.o) |
| CONFIG_SPL_FS_EXT4 |
| CONFIG_SPL_LIBGENERIC_SUPPORT (lib/libgeneric.o) |
| CONFIG_SPL_POWER (drivers/power/libpower.o) |
| CONFIG_SPL_NAND_SUPPORT (drivers/mtd/nand/raw/libnand.o) |
| CONFIG_SPL_DRIVERS_MISC (drivers/misc) |
| CONFIG_SPL_DMA (drivers/dma/libdma.o) |
| CONFIG_SPL_POST_MEM_SUPPORT (post/drivers/memory.o) |
| CONFIG_SPL_NAND_LOAD (drivers/mtd/nand/raw/nand_spl_load.o) |
| CONFIG_SPL_SPI_LOAD (drivers/mtd/spi/spi_spl_load.o) |
| CONFIG_SPL_RAM_DEVICE (common/spl/spl.c) |
| CONFIG_SPL_WATCHDOG (drivers/watchdog/libwatchdog.o) |
| CONFIG_SPL_SYSCON (drivers/core/syscon-uclass.o) |
| CONFIG_SPL_GZIP (lib/gzip.o) |
| CONFIG_SPL_VIDEO (drivers/video/video-uclass.o drivers/video/vidconsole-uclass.o) |
| CONFIG_SPL_SPLASH_SCREEN (common/splash.o) |
| CONFIG_SPL_SPLASH_SOURCE (common/splash_source.o) |
| CONFIG_SPL_GPIO (drivers/gpio) |
| CONFIG_SPL_DM_GPIO (drivers/gpio/gpio-uclass.o) |
| CONFIG_SPL_BMP (drivers/video/bmp.o) |
| CONFIG_SPL_BLOBLIST (common/bloblist.o) |
| |
| Adding xPL-specific code |
| ------------------------ |
| |
| To check whether a feature is enabled, use CONFIG_IS_ENABLED():: |
| |
| if (CONFIG_IS_ENABLED(CLK)) |
| ... |
| |
| This checks CONFIG_CLK for the main build, CONFIG_SPL_CLK for the SPL build, |
| CONFIG_TPL_CLK for the TPL build, etc. |
| |
| U-Boot Boot Phases |
| ------------------ |
| |
| U-Boot goes through the following boot phases where TPL, VPL, SPL are optional. |
| While many boards use SPL, fewer use TPL. |
| |
| TPL |
| Very early init, as tiny as possible. This loads SPL (or VPL if enabled). |
| |
| VPL |
| Optional verification step, which can select one of several SPL binaries, |
| if A/B verified boot is enabled. Implementation of the VPL logic is |
| work-in-progress. For now it just boots into SPL. |
| |
| SPL |
| Secondary program loader. Sets up SDRAM and loads U-Boot proper. It may also |
| load other firmware components. |
| |
| U-Boot |
| U-Boot proper, containing the command line and boot logic. |
| |
| Further usages of U-Boot SPL comprise: |
| |
| * Launching BL31 of ARM Trusted Firmware which invokes main U-Boot as BL33 |
| * launching EDK II |
| * launching Linux kernel |
| * launching RISC-V OpenSBI which invokes main U-Boot |
| |
| Checking the boot phase |
| ----------------------- |
| |
| Use `xpl_phase()` to find the current U-Boot phase, e.g. `PHASE_SPL`. You can |
| also find the previous and next phase and get the phase name. |
| |
| |
| .. _fdtgrep_filter: |
| |
| Device tree |
| ----------- |
| The U-Boot device tree is filtered by the fdtgrep tools during the build |
| process to generate a much smaller device tree used in SPL (spl/u-boot-spl.dtb) |
| with: |
| |
| - the mandatory nodes (/alias, /chosen, /config) |
| - the nodes with one pre-relocation property: |
| 'bootph-all' or 'bootph-pre-ram' |
| |
| fdtgrep is also used to remove: |
| |
| - the properties defined in CONFIG_OF_SPL_REMOVE_PROPS |
| - all the pre-relocation properties |
| ('bootph-all', 'bootph-pre-ram' (SPL), 'bootph-pre-sram' (TPL) and |
| 'bootph-verify' (TPL)) |
| |
| All the nodes remaining in the SPL devicetree are bound |
| (see doc/driver-model/design.rst). |
| |
| NOTE: U-Boot migrated to a new schema for the u-boot,dm-* tags in 2023. Please |
| update to use the new bootph-* tags as described in the |
| doc/device-tree-bindings/bootph.yaml binding file. |
| |
| Debugging |
| --------- |
| |
| When building SPL with DEBUG set you may also need to set CONFIG_PANIC_HANG |
| as in most cases do_reset is not defined within SPL. |
| |
| |
| Estimating stack usage |
| ---------------------- |
| |
| With gcc 4.6 (and later) and the use of GNU cflow it is possible to estimate |
| stack usage at various points in run sequence of SPL. The -fstack-usage option |
| to gcc will produce '.su' files (such as arch/arm/cpu/armv7/syslib.su) that |
| will give stack usage information and cflow can construct program flow. |
| |
| Must have gcc 4.6 or later, which supports -fstack-usage: |
| |
| #. Build normally |
| #. Perform the following shell command to generate a list of C files used in |
| SPL: |
| #. `find spl -name '*.su' | sed -e 's:^spl/::' -e 's:[.]su$:.c:' > used-spl.list` |
| #. Execute cflow: |
| `$ cflow --main=board_init_r $(cat used-spl.list) 2>&1 | $PAGER` |
| |
| cflow will spit out a number of warnings as it does not parse |
| the config files and picks functions based on #ifdef. Parsing the '.i' |
| files instead introduces another set of headaches. These warnings are |
| not usually important to understanding the flow, however. |
| |
| |
| Reserving memory in xPL |
| ----------------------- |
| |
| If memory needs to be reserved in RAM during an xPL phase with the requirement |
| that the xPL reserved memory remains preserved across further boot phases too |
| then it needs to be reserved mandatorily starting from end of RAM. This is to |
| ensure that further phases can simply skip this region before carrying out |
| further reservations or updating the relocation address. |
| |
| Also out of these regions which are to be preserved across further phases of |
| boot, video framebuffer memory region must be reserved first starting from |
| end of RAM for which the helper function spl_reserve_video_from_ram_top() is |
| provided |
| which makes sure that video memory is placed at the top of reservation area with |
| further reservations below it. |
| |
| The reservation information for these regions can be passed to the |
| further boot phases using a bloblist. For e.g. the information for the |
| framebuffer area reserved by xPL can be passed onto U-Boot using |
| BLOBLISTT_U_BOOT_VIDEO |
| |
| The further boot phases need to parse each of the blobs passed from xPL phase |
| starting from video bloblist and skip this whole xPL reserved-memory area from |
| end of RAM as per the blobs received, before carrying out further |
| reservations or updating the relocation address. For e.g, U-Boot proper uses |
| function setup_relocaddr_from_bloblist() to parse the bloblist passed from |
| previous phase and skip the memory reserved from previous phase accordingly. |