[U-Boot] [PATCH 3/3] doc: SPL: Add README for secure boot support

[Sumit Garg]

Adds information regarding SPL handling validation process of main u-boot
image on power/mpc85xx and arm/layerscape platforms.

Signed-off-by: Sumit Garg <sumit.garg at nxp.com>
---

Changes PATCH v5->PATCH v6:
Added README for SECURE BOOT support in SPL framework.

 doc/SPL/README.spl-secure-boot | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 doc/SPL/README.spl-secure-boot

diff --git a/doc/SPL/README.spl-secure-boot b/doc/SPL/README.spl-secure-boot
new file mode 100644
index 0000000..f2f8d78
--- /dev/null
+++ b/doc/SPL/README.spl-secure-boot
@@ -0,0 +1,18 @@
+Overview of SPL verified boot on powerpc/mpc85xx & arm/layerscape platforms
+===========================================================================
+
+Introduction
+------------
+
+This document provides an overview of how SPL verified boot works on powerpc/
+mpc85xx & arm/layerscape platforms.
+
+Methodology
+-----------
+
+The SPL image is responsible for loading the next stage boot loader, which is
+the main u-boot image. For secure boot process on these platforms ROM verifies
+SPL image, so to continue chain of trust SPL image verifies U-boot image using
+spl_validate_uboot(). This function uses QorIQ Trust Architecture header
+(appended to U-boot image) to validate the U-boot binary just before passing
+control to it.
-- 
1.8.1.4