From f945327adf24bafde599a68c93d4f0ad3ee80160 Mon Sep 17 00:00:00 2001 From: Heinrich Schuchardt Date: Fri, 28 Jul 2023 18:44:34 +0200 Subject: [PATCH] doc: U-Boot boot phases Add more detail to the description of U-Boot boot phases: * describe which steps are optional * mentions alternative boot flows Signed-off-by: Heinrich Schuchardt Reviewed-by: Bin Meng --- doc/develop/spl.rst | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/doc/develop/spl.rst b/doc/develop/spl.rst index a1515a7b43..76e87f07c7 100644 --- a/doc/develop/spl.rst +++ b/doc/develop/spl.rst @@ -77,10 +77,11 @@ To check whether a feature is enabled, use CONFIG_IS_ENABLED():: 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 Boot Phases +------------------ -U-Boot boots through the following 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). @@ -97,6 +98,12 @@ SPL 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 ----------------------- -- 2.39.5