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binman: Add documentation for the symbol feature

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Add this feature to the README.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
This commit is contained in:
Simon Glass 2017-11-13 18:55:05 -07:00
parent dfce1799e7
commit 39c1502ccc
1 changed files with 31 additions and 1 deletions
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32
tools/binman/README
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@ -439,6 +439,8 @@ contents of an entry in some way. For example, it would be possible to create
an entry containing a hash of the contents of some other entries. At this
stage the position and size of entries should not be adjusted.
6. WriteEntryInfo()
7. BuildImage() - builds the image and writes it to a file. This is the final
step.
@ -471,6 +473,33 @@ the 'warning' line in scripts/Makefile.lib to see what it has found:
# u_boot_dtsi_options_debug = $(u_boot_dtsi_options_raw)
Access to binman entry positions at run time
--------------------------------------------
Binman assembles images and determines where each entry is placed in the image.
This information may be useful to U-Boot at run time. For example, in SPL it
is useful to be able to find the location of U-Boot so that it can be executed
when SPL is finished.
Binman allows you to declare symbols in the SPL image which are filled in
with their correct values during the build. For example:
binman_sym_declare(ulong, u_boot_any, pos);
declares a ulong value which will be assigned to the position of any U-Boot
image (u-boot.bin, u-boot.img, u-boot-nodtb.bin) that is present in the image.
You can access this value with something like:
ulong u_boot_pos = binman_sym(ulong, u_boot_any, pos);
Thus u_boot_pos will be set to the position of U-Boot in memory, assuming that
the whole image has been loaded, or is available in flash. You can then jump to
that address to start U-Boot.
At present this feature is only supported in SPL. In principle it is possible
to fill in such symbols in U-Boot proper, as well.
Code coverage
-------------
@ -543,7 +572,8 @@ To do
Some ideas:
- Fill out the device tree to include the final position and size of each
entry (since the input file may not always specify these)
entry (since the input file may not always specify these). See also
'Access to binman entry positions at run time' above
- Use of-platdata to make the information available to code that is unable
to use device tree (such as a very small SPL image)
- Write an image map to a text file