Merge tag 'doc-next-2025-09-27' of https://source.denx.de/u-boot/custodians/u-boot-efi into next

Pull request doc-next-2025-09-27

CI:

* https://source.denx.de/u-boot/custodians/u-boot-efi/-/pipelines/27746

Documentation:

* Move ext4 documentation to HTML.
* Describe configuration option EXT4_MAX_JOURNAL_ENTRIES and
  memory ext4 journal memory requirements.

2 files changed, 145 insertions, 0 deletions

diff --git a/doc/usage/filesystems/ext4.rst b/doc/usage/filesystems/ext4.rst
new file mode 100644
index 00000000000..c6cdaf57fac
--- /dev/null
+++ b/doc/usage/filesystems/ext4.rst
@@ -0,0 +1,137 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Ext4 File System
+================
+
+Overview
+--------
+
+U-Boot supports access of both ext2 and ext4 filesystems, either in read-only
+mode or in read-write mode.
+
+Configuration
+-------------
+
+First, to enable support for both ext4 (and, automatically, ext2 as well),
+but without selecting the corresponding commands, enable one of the following:
+
+::
+
+  CONFIG_FS_EXT4	(for read-only)
+  CONFIG_EXT4_WRITE	(for read-write)
+
+Next, to select the ext2-related commands:
+
+  * ext2ls
+  * ext2load
+
+or ext4-related commands:
+
+  * ext4size
+  * ext4ls
+  * ext4load
+
+use one or both of:
+
+::
+
+	CONFIG_CMD_EXT2
+	CONFIG_CMD_EXT4
+
+Selecting either of the above automatically selects CONFIG_FS_EXT4 if it
+wasn't enabled already.
+
+In addition, to get the write access command ``ext4write``, enable:
+
+::
+
+	CONFIG_CMD_EXT4_WRITE
+
+which automatically selects CONFIG_EXT4_WRITE if it wasn't defined
+already.
+
+Also relevant are the generic filesystem commands, selected by:
+
+::
+
+	CONFIG_CMD_FS_GENERIC
+
+This does not automatically enable EXT4 support for you, you still need
+to do that yourself.
+
+Lastly, the current u-boot implementation for Ext4 write requires a lot
+of memory to run successfully. The following enable support for
+large Ext4 partitions:
+
+::
+
+	CONFIG_EXT4_MAX_JOURNAL_ENTRIES
+	CONFIG_SYS_MALLOC_LEN
+
+The number of journal entries and dynamic memory allocation are proportional
+to the partition capacity. For example, an ext4 4TB HDD partition could
+require approximately 500 entries and more than 128 MB heap space.
+
+Examples
+--------
+
+Some sample commands to test ext4 support:
+
+1. Check that the ext4 commands can be seen in the output of U-Boot help:
+
+::
+
+	=> help
+	...
+	ext4load- load binary file from a Ext4 file system
+	ext4ls  - list files in a directory (default /)
+	ext4size - determine a file's size
+	ext4write- create a file in ext4 formatted partition
+	...
+
+2. The ``ext4ls`` command can be used to list the files in an ext4-formatted partition:
+
+::
+
+	ext4ls <interface> <dev[:part]> [directory]
+
+For example, to list files in ext4-formatted partition directory /usr/lib:
+
+::
+
+	=> ext4ls mmc 0:5 /usr/lib
+
+3. The ``ext4load`` command can be used to read and load a file from an
+ext4-formatted partition to RAM:
+
+::
+
+	ext4load <interface> [<dev[:part]> [addr [filename [bytes [pos]]]]]
+
+For example, to load file /uImage from an ext4-formatted partition:
+
+::
+
+	=> ext4load mmc 2:2 0x30007fc0 uImage
+
+4. The ``ext4write`` command can be used to write to an ext4 partition:
+
+::
+
+	ext4write <interface> <dev[:part]> <addr> <absolute filename path> [sizebytes] [file offset]
+
+For example, to write a file loaded at 0x8200000 of size 256 bytes to an
+ext4-formatted partition with the filename ``/boot/sample_file.hex``:
+
+::
+
+	=> ext4write mmc 2:2 0x82000000 /boot/sample_file.hex 0x100
+	256 bytes written in 138 ms (1000 Bytes/s)
+
+
+References
+----------
+
+	* ext4 implementation in Linux Kernel
+	* Uboot existing ext2 load and ls implementation
+	* Journaling block device JBD2 implementation in linux Kernel
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 3a48521d5d5..4b0533c8e69 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -147,3 +147,11 @@ Booting OS
 
    os/plan9
    os/vxworks
+
+File Systems
+------------
+
+.. toctree::
+   :maxdepth: 1
+
+   filesystems/ext4