doc: Update SPL docs for the xPL changes

Update the various references to SPL in this document. Make sure to
refer to 'phases' instead of 'stages', which is not a U-Boot term.

Fix a few U-boot typos and try to improve grammar a little while we are
here.

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 41 insertions, 38 deletions

diff --git a/doc/develop/spl.rst b/doc/develop/spl.rst
index a92110e4fa9..aa6d28fa333 100644
--- a/doc/develop/spl.rst
+++ b/doc/develop/spl.rst
@@ -1,11 +1,12 @@
-Generic SPL framework
+Generic xPL 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
+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.
 
@@ -13,38 +14,39 @@ 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.
+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_SPL_BUILD is enabled by Kconfig for SPL.
-Source files can therefore be compiled for SPL with different settings.
+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 ($(CONFIG_SPL_BUILD),y)
+   ifeq ($(CONFIG_XPL_BUILD),y)
    obj-y += board_spl.o
    else
    obj-y += board.o
    endif
 
-   obj-$(CONFIG_SPL_BUILD) += foo.o
+   obj-$(CONFIG_XPL_BUILD) += foo.o
 
-   #ifdef CONFIG_SPL_BUILD
+   if (IS_ENABLED(CONFIG_XPL_BUILD))
            foo();
-   #endif
 
    if (xpl_phase() == PHASE_TPL)
            bar();
 
-The building of SPL images can be enabled by CONFIG_SPL option in Kconfig.
+The building of xPL images can be enabled by CONFIG_SPL (etc.) options 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.
+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 SPL binary one can
-optionally define CONFIG_SPL_XXX_SUPPORT. Currently following options
+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)
@@ -77,7 +79,7 @@ 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
+Adding xPL-specific code
 ------------------------
 
 To check whether a feature is enabled, use CONFIG_IS_ENABLED()::
@@ -92,7 +94,7 @@ 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.
+While many boards use SPL, fewer use TPL.
 
 TPL
    Very early init, as tiny as possible. This loads SPL (or VPL if enabled).
@@ -179,29 +181,30 @@ files instead introduces another set of headaches.  These warnings are
 not usually important to understanding the flow, however.
 
 
-Reserving memory in SPL
+Reserving memory in xPL
 -----------------------
 
-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
+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 stages can simply skip this region before carrying out
+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 stages of
+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 helper function spl_reserve_video_from_ram_top is provided
-which makes sure that video memory is placed at top of reservation area with
+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 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.
+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.