doc: Move external FIT docs into the main body

Rather than having this as an addition to the end, move this into the
main body of the spec, rewriting as needed.

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

1 files changed, 38 insertions, 36 deletions

diff --git a/doc/usage/fit/source_file_format.rst b/doc/usage/fit/source_file_format.rst
index 1c72230..f1cc1bc 100644
--- a/doc/usage/fit/source_file_format.rst
+++ b/doc/usage/fit/source_file_format.rst
@@ -81,6 +81,25 @@ is used as it's identifier as it assures uniqueness without additional
 checking required.
 
 
+External data
+~~~~~~~~~~~~~
+
+FIT is normally built initially with image data in the 'data' property of each
+image node. It is also possible for this data to reside outside the FIT itself.
+This allows the 'FDT' part of the FIT to be quite small, so that it can be
+loaded and scanned without loading a large amount of data. Then when an image is
+needed it can be loaded from an external source.
+
+External FITs use 'data-offset' or 'data-position' instead of 'data'.
+
+The mkimage tool can convert a FIT to use external data using the `-E` argument,
+optionally using `-p` to specific a fixed position.
+
+It is often desirable to align each image to a block size or cache-line size
+(e.g. 512 bytes), so that there is no need to copy it to an aligned address when
+reading the image data. The mkimage tool provides a `-B` argument to support
+this.
+
 Root-node properties
 --------------------
 
@@ -215,9 +234,6 @@ type
     zynqmpimage           Xilinx ZynqMP Boot Image }
     ====================  ==================
 
-data
-    Path to the external file which contains this node's binary data.
-
 compression
     Compression used by included data. If no compression is used, the
     compression property should be set to "none". If the data is compressed but
@@ -238,9 +254,28 @@ compression
     zstd                  zstd compressed
     ====================  ==================
 
+data-size
+    size of the data in bytes
+
+
 Conditionally mandatory property
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+data
+    Path to the external file which contains this node's binary data. Within
+    the FIT this is the contents of the file. This is mandatory unless
+    external data is used.
+
+data-offset
+    Offset of the data in a separate image store. The image store is placed
+    immediately after the last byte of the device tree binary, aligned to a
+    4-byte boundary. This is mandatory if external data is used, with an offset.
+
+data-position
+    Machine address at which the data is to be found. This is a fixed address
+    not relative to the loading of the FIT. This is mandatory if external data
+    used with a fixed address.
+
 os
     OS name, mandatory for types "kernel". Valid OS names are:
 
@@ -478,39 +513,6 @@ Older, 2.4 kernel and 2.6 non-FDT kernel do not use FDT blob, in such cases
 not* be specified in a configuration node.
 
 
-External data
--------------
-
-The above format shows a 'data' property which holds the data for each image.
-It is also possible for this data to reside outside the FIT itself. This
-allows the FIT to be quite small, so that it can be loaded and scanned
-without loading a large amount of data. Then when an image is needed it can
-be loaded from an external source.
-
-In this case the 'data' property is omitted. Instead you can use:
-
-data-offset
-    offset of the data in a separate image store. The image
-    store is placed immediately after the last byte of the device tree binary,
-    aligned to a 4-byte boundary.
-
-data-size
-    size of the data in bytes
-
-The 'data-offset' property can be substituted with 'data-position', which
-defines an absolute position or address as the offset. This is helpful when
-booting U-Boot proper before performing relocation. Pass '-p [offset]' to
-mkimage to enable 'data-position'.
-
-Normal kernel FIT image has data embedded within FIT structure. U-Boot image
-for SPL boot has external data. Existence of 'data-offset' can be used to
-identify which format is used.
-
-For FIT image with external data, it would be better to align each blob of data
-to block(512 byte) for block device, so that we don't need to do the copy when
-read the image data in SPL. Pass '-B 0x200' to mkimage to align the FIT
-structure and data to 512 byte, other values available for other align size.
-
 Examples
 --------