doc: Move existing rst files into api sub-directory

Currently the Sphinx doc only contains API descriptions of several
U-Boot subsystems. For future extension, group these existing docs
into an API sub-directory.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

4 files changed, 223 insertions, 0 deletions

diff --git a/doc/api/efi.rst b/doc/api/efi.rst
new file mode 100644
index 00000000000..39e2dbae0bc
--- /dev/null
+++ b/doc/api/efi.rst
@@ -0,0 +1,105 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+UEFI subsystem
+==============
+
+Lauching UEFI images
+--------------------
+
+Bootefi command
+~~~~~~~~~~~~~~~
+
+The bootefi command is used to start UEFI applications or to install UEFI
+drivers. It takes two parameters
+
+    bootefi <image address> [fdt address]
+
+* image address - the memory address of the UEFI binary
+* fdt address - the memory address of the flattened device tree
+
+The environment variable 'bootargs' is passed as load options in the UEFI system
+table. The Linux kernel EFI stub uses the load options as command line
+arguments.
+
+.. kernel-doc:: cmd/bootefi.c
+   :internal:
+
+Boot manager
+~~~~~~~~~~~~
+
+The UEFI specification foresees to define boot entries and boot sequence via UEFI
+variables. Booting according to these variables is possible via
+
+    bootefi bootmgr [fdt address]
+
+* fdt address - the memory address of the flattened device tree
+
+The relevant variables are:
+
+* Boot0000-BootFFFF define boot entries
+* BootNext specifies next boot option to be booted
+* BootOrder specifies in which sequence the boot options shall be tried if
+  BootNext is not defined or booting via BootNext fails
+
+.. kernel-doc:: lib/efi_loader/efi_bootmgr.c
+   :internal:
+
+Efidebug command
+~~~~~~~~~~~~~~~~
+
+The efidebug command is used to set and display boot options as well as to
+display information about internal data of the UEFI subsystem (devices,
+drivers, handles, loaded images, and the memory map).
+
+.. kernel-doc:: cmd/efidebug.c
+   :internal:
+
+Initialization of the UEFI sub-system
+-------------------------------------
+
+.. kernel-doc:: lib/efi_loader/efi_setup.c
+   :internal:
+
+Boot services
+-------------
+
+.. kernel-doc:: lib/efi_loader/efi_boottime.c
+   :internal:
+
+Image relocation
+~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: lib/efi_loader/efi_image_loader.c
+   :internal:
+
+Memory services
+~~~~~~~~~~~~~~~
+
+.. kernel-doc:: lib/efi_loader/efi_memory.c
+   :internal:
+
+Runtime services
+----------------
+
+.. kernel-doc:: lib/efi_loader/efi_runtime.c
+   :internal:
+
+Variable services
+~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: lib/efi_loader/efi_variable.c
+   :internal:
+
+UEFI drivers
+------------
+
+UEFI driver uclass
+~~~~~~~~~~~~~~~~~~
+.. kernel-doc:: lib/efi_driver/efi_uclass.c
+   :internal:
+
+Block device driver
+~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: lib/efi_driver/efi_block_device.c
+   :internal:
diff --git a/doc/api/index.rst b/doc/api/index.rst
new file mode 100644
index 00000000000..d484c066c59
--- /dev/null
+++ b/doc/api/index.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot API documentation
+========================
+
+.. toctree::
+   :maxdepth: 2
+
+   efi
+   linker_lists
+   serial
diff --git a/doc/api/linker_lists.rst b/doc/api/linker_lists.rst
new file mode 100644
index 00000000000..72f514e0ac0
--- /dev/null
+++ b/doc/api/linker_lists.rst
@@ -0,0 +1,100 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Linker-Generated Arrays
+=======================
+
+A linker list is constructed by grouping together linker input
+sections, each containing one entry of the list. Each input section
+contains a constant initialized variable which holds the entry's
+content. Linker list input sections are constructed from the list
+and entry names, plus a prefix which allows grouping all lists
+together. Assuming _list and _entry are the list and entry names,
+then the corresponding input section name is
+
+::
+
+  .u_boot_list_ + 2_ + @_list + _2_ + @_entry
+
+and the C variable name is
+
+::
+
+  _u_boot_list + _2_ + @_list + _2_ + @_entry
+
+This ensures uniqueness for both input section and C variable name.
+
+Note that the names differ only in the first character, "." for the
+section and "_" for the variable, so that the linker cannot confuse
+section and symbol names. From now on, both names will be referred
+to as
+
+::
+
+  %u_boot_list_ + 2_ + @_list + _2_ + @_entry
+
+Entry variables need never be referred to directly.
+
+The naming scheme for input sections allows grouping all linker lists
+into a single linker output section and grouping all entries for a
+single list.
+
+Note the two '_2_' constant components in the names: their presence
+allows putting a start and end symbols around a list, by mapping
+these symbols to sections names with components "1" (before) and
+"3" (after) instead of "2" (within).
+Start and end symbols for a list can generally be defined as
+
+::
+
+  %u_boot_list_2_ + @_list + _1_...
+  %u_boot_list_2_ + @_list + _3_...
+
+Start and end symbols for the whole of the linker lists area can be
+defined as
+
+::
+
+  %u_boot_list_1_...
+  %u_boot_list_3_...
+
+Here is an example of the sorted sections which result from a list
+"array" made up of three entries : "first", "second" and "third",
+iterated at least once.
+
+::
+
+  .u_boot_list_2_array_1
+  .u_boot_list_2_array_2_first
+  .u_boot_list_2_array_2_second
+  .u_boot_list_2_array_2_third
+  .u_boot_list_2_array_3
+
+If lists must be divided into sublists (e.g. for iterating only on
+part of a list), one can simply give the list a name of the form
+'outer_2_inner', where 'outer' is the global list name and 'inner'
+is the sub-list name. Iterators for the whole list should use the
+global list name ("outer"); iterators for only a sub-list should use
+the full sub-list name ("outer_2_inner").
+
+Here is an example of the sections generated from a global list
+named "drivers", two sub-lists named "i2c" and "pci", and iterators
+defined for the whole list and each sub-list:
+
+::
+
+  %u_boot_list_2_drivers_1
+  %u_boot_list_2_drivers_2_i2c_1
+  %u_boot_list_2_drivers_2_i2c_2_first
+  %u_boot_list_2_drivers_2_i2c_2_first
+  %u_boot_list_2_drivers_2_i2c_2_second
+  %u_boot_list_2_drivers_2_i2c_2_third
+  %u_boot_list_2_drivers_2_i2c_3
+  %u_boot_list_2_drivers_2_pci_1
+  %u_boot_list_2_drivers_2_pci_2_first
+  %u_boot_list_2_drivers_2_pci_2_second
+  %u_boot_list_2_drivers_2_pci_2_third
+  %u_boot_list_2_drivers_2_pci_3
+  %u_boot_list_2_drivers_3
+
+.. kernel-doc:: include/linker_lists.h
+   :internal:
diff --git a/doc/api/serial.rst b/doc/api/serial.rst
new file mode 100644
index 00000000000..ed34e592a44
--- /dev/null
+++ b/doc/api/serial.rst
@@ -0,0 +1,7 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Serial system
+=============
+
+.. kernel-doc:: drivers/serial/serial.c
+   :internal: