aaeb330cac
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
|
|
=====================
|
|
|
|
Overview
|
|
--------
|
|
|
|
To unify all existing implementations for a secondary program loader (SPL)
|
|
and to allow simply adding of new implementations this generic SPL 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 SPL are built separately and placed in the "spl" directory.
|
|
The final binaries which are generated are u-boot-spl, u-boot-spl.bin and
|
|
u-boot-spl.map.
|
|
|
|
A config option named CONFIG_SPL_BUILD is enabled by Kconfig for SPL.
|
|
Source files can therefore be compiled for SPL with different settings.
|
|
|
|
For example::
|
|
|
|
ifeq ($(CONFIG_SPL_BUILD),y)
|
|
obj-y += board_spl.o
|
|
else
|
|
obj-y += board.o
|
|
endif
|
|
|
|
obj-$(CONFIG_SPL_BUILD) += foo.o
|
|
|
|
#ifdef CONFIG_SPL_BUILD
|
|
foo();
|
|
#endif
|
|
|
|
|
|
The building of SPL images can be enabled by CONFIG_SPL option in Kconfig.
|
|
|
|
Because SPL images normally have a different text base, one has to be
|
|
configured by defining CONFIG_SPL_TEXT_BASE. The linker script has to be
|
|
defined with CONFIG_SPL_LDSCRIPT.
|
|
|
|
To support generic U-Boot libraries and drivers in the SPL binary one can
|
|
optionally define CONFIG_SPL_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 SPL-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, less 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 `spl_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.
|
|
|
|
|
|
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 SPL
|
|
-----------------------
|
|
|
|
If memory needs to be reserved in RAM during SPL stage with the requirement that
|
|
the SPL reserved memory remains preserved across further boot stages too
|
|
then it needs to be reserved mandatorily starting from end of RAM. This is to
|
|
ensure that further stages 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 stages of
|
|
boot, video framebuffer memory region must be reserved first starting from
|
|
end of RAM for which helper function spl_reserve_video_from_ram_top is provided
|
|
which makes sure that video memory is placed at top of reservation area with
|
|
further reservations below it.
|
|
|
|
The corresponding information of reservation for those regions can be passed to
|
|
further boot stages using a bloblist. For e.g. the information for
|
|
framebuffer area reserved by SPL can be passed onto U-boot using
|
|
BLOBLISTT_U_BOOT_VIDEO.
|
|
|
|
The further boot stages need to parse each of the bloblist passed from SPL stage
|
|
starting from video bloblist and skip this whole SPL reserved memory area from
|
|
end of RAM as per the bloblists 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 bloblists passed from
|
|
previous stage and skip the memory reserved from previous stage accordingly.
|