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doc: Expand SPL docs to explain the phase and config

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Add a bit more information about how to use SPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass 2022-04-30 00:56:46 -06:00 committed by Tom Rini
parent d411359d91
commit a36d251b50
1 changed files with 34 additions and 0 deletions
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34
doc/develop/spl.rst
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@ -66,6 +66,40 @@ 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)
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 Phases
-------------
U-Boot boots through the following phases:
TPL
Very early init, as tiny as possible. This loads 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.
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