spl: fit: Add support for applying DT overlay

doc/uImage.FIT/overlay-fdt-boot.txt is describing how to create FIT
image with DT overlays in it.
Add support for this feature to SPL.

Here is the ZynqMP fragment where dtb points to full DT and dtbo is
overlay which should be applied on the top of dtb.
config {
        description = "ATF with full u-boot overlay";
        firmware = "atf";
        loadables = "uboot";
        fdt = "dtb", "dtbo";
};

The whole feature depends on OF_LIBFDT_OVERLAY which is adding +4kB code
and 0 for platforms which are not enabling this feature.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/Kconfig b/Kconfig
index 46a31f45b9..0edd4ec2b0 100644
--- a/Kconfig
+++ b/Kconfig
@@ -444,6 +444,15 @@ config SPL_LOAD_FIT
 	  particular it can handle selecting from multiple device tree
 	  and passing the correct one to U-Boot.
 
+config SPL_LOAD_FIT_APPLY_OVERLAY
+	bool "Enable SPL applying DT overlays from FIT"
+	depends on SPL_LOAD_FIT
+	select OF_LIBFDT_OVERLAY
+	help
+	  The device tree is loaded from the FIT image. Allow the SPL is to
+	  also load device-tree overlays from the FIT image an apply them
+	  over the device tree.
+
 config SPL_LOAD_FIT_FULL
 	bool "Enable SPL loading U-Boot as a FIT (full fitImage features)"
 	select SPL_FIT