[PATCH v2] ARM: Distro boot: document the need for fdtfile variable to be set

[dgilmore at redhat.com]

From: Dennis Gilmore <dennis at ausil.us>

When testing builds provided in https://github.com/openwrt/openwrt/pull/3360
I discovered that fdtfile was not set and as a result the firmware was not
functional. So I am documenting what is needed.

Signed-off-by: Dennis Gilmore <dennis at ausil.us>

Cc: Atish Patra <atish.patra at wdc.com>
Cc: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
Cc: Tom Rini <trini at konsulko.com>
Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
Cc: Vagrant Cascadian <vagrant at debian.org>
Cc: Stephen Warren <swarren at nvidia.com>
Cc: Karsten Merker <merker at debian.org>
---
 doc/README.distro | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/doc/README.distro b/doc/README.distro
index 5076bebd18..cc1c41ecb3 100644
--- a/doc/README.distro
+++ b/doc/README.distro
@@ -224,6 +224,17 @@ fdt_addr_r:
 
   A size of 1MB for the FDT/DTB seems reasonable.
 
+fdtfile:
+
+  Mandatory. the name of the DTB file for the specific board for instance
+  the espressobin v5 board the value is "marvell/armada-3720-espressobin.dtb"
+  while on a clearfog pro it is "armada-388-clearfog-pro.dtb" in the case of
+  a board providing its firmware based DTB this value can be used to override
+  the DTB with a different DTB. fdtfile will automatically be set for you if
+  it matches the format ${soc}-${board}.dtb which covers most 32 bit use cases.
+  AArch64 generally does not match as the Linux kernel put the dtb files under
+  SoC vendor directories. 
+
 ramdisk_addr_r:
 
   Mandatory. The location in RAM where the initial ramdisk will be loaded to
-- 
2.28.0