fdt: Add option to default to most compatible conf in a fit image

When booting a fit image with multiple configurations, the user either has to
specify which configuration to use explicitly, or there has to be a default
defined which is chosen automatically. This change adds an option to change
that behavior so that a configuration can be selected explicitly, or the
configuration which has the device tree that claims to be compatible with the
earliest item in U-Boot's device tree.

In other words, if U-Boot claimed to be compatible with A, B, and then C, and
the configurations claimed to be compatible with A, D and B, D and D, E, the
first configuration, A, D, would be chosen. Both the first and second
configurations match, but the first one matches a more specific entry in
U-Boot's device tree. The order in the kernel's device tree is ignored.

Signed-off-by: Gabe Black <gabeblack@google.com>

Commit-Ready: Gabe Black <gabeblack@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/README b/README
index afdf591..6c77842 100644
--- a/README
+++ b/README
@@ -2597,6 +2597,17 @@ FIT uImage format:
  -150	common/cmd_nand.c	Incorrect FIT image format
   151	common/cmd_nand.c	FIT image format OK
 
+- FIT image support:
+		CONFIG_FIT
+		Enable support for the FIT uImage format.
+
+		CONFIG_FIT_BEST_MATCH
+		When no configuration is explicitly selected, default to the
+		one whose fdt's compatibility field best matches that of
+		U-Boot itself. A match is considered "best" if it matches the
+		most specific compatibility entry of U-Boot's fdt's root node.
+		The order of entries in the configuration's fdt is ignored.
+
 - Standalone program support:
 		CONFIG_STANDALONE_LOAD_ADDR