mkimage: Support placing data outside the FIT

One limitation of FIT is that all the data is 'inline' within it, using a
'data' property in each image node. This means that to find out what is in
the FIT it is necessary to scan the entire file. Once loaded it can be
scanned and then the images can be copied to the correct place in memory.

In SPL it can take a significant amount of time to copy images around in
memory. Also loading data that does not end up being used is wasteful. It
would be useful if the FIT were small, acting as a directory, with the
actual data stored elsewhere.

This allows SPL to load the entire FIT, without the images, then load the
images it wants later.

Add a -E option to mkimage to request that it output an 'external' FIT.

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

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/mkimage.1 b/doc/mkimage.1
index 036b095..e0f210a 100644
--- a/doc/mkimage.1
+++ b/doc/mkimage.1
@@ -112,6 +112,15 @@ Provide special options to the device tree compiler that is used to
 create the image.
 
 .TP
+.BI "\-E
+After processing, move the image data outside the FIT and store a data offset
+in the FIT. Images will be placed one after the other immediately after the
+FIT, with each one aligned to a 4-byte boundary. The existing 'data' property
+in each image will be replaced with 'data-offset' and 'data-size' properties.
+A 'data-offset' of 0 indicates that it starts in the first (4-byte aligned)
+byte after the FIT.
+
+.TP
 .BI "\-f [" "image tree source file" " | " "auto" "]"
 Image tree source file that describes the structure and contents of the
 FIT image.