board: amlogic: document alternative libretech-cc installation methods

As already documented in this README, several binaries must be
glued together in order to boot the device.

Extend the documentation to cover the prebuilt binaries
(saving you the hassle of installing ancient cross-compilers),
and also mention the open source replacements for the encryption
tool (which is especially useful if you want to avoid requiring
32-bit x86 binaries in your build system).

Signed-off-by: Daniel Drake <drake@endlessm.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

1 files changed, 37 insertions, 4 deletions

diff --git a/board/amlogic/p212/README.libretech-cc b/board/amlogic/p212/README.libretech-cc
index d007f58764..6af7de3cfa 100644
--- a/board/amlogic/p212/README.libretech-cc
+++ b/board/amlogic/p212/README.libretech-cc
@@ -38,9 +38,28 @@ U-Boot compilation
 Image creation
 ==============
 
-Amlogic doesn't provide sources for the firmware and for tools needed
-to create the bootloader image, so it is necessary to obtain them from
-the git tree published by the board vendor:
+To boot the system, u-boot must be combined with several earlier stage
+bootloaders:
+
+* bl2.bin: vendor-provided binary blob
+* bl21.bin: built from vendor u-boot source
+* bl30.bin: vendor-provided binary blob
+* bl301.bin: built from vendor u-boot source
+* bl31.bin: vendor-provided binary blob
+* acs.bin: built from vendor u-boot source
+
+These binaries and the tools required below have been collected and prebuilt
+for convenience at <https://github.com/BayLibre/u-boot/releases/>
+
+Download and extract the libretech-cc release from there, and set FIPDIR to
+point to the `fip` subdirectory.
+
+ > export FIPDIR=/path/to/extracted/fip
+
+Alternatively, you can obtain the original vendor u-boot tree which
+contains the required blobs and sources, and build yourself.
+Note that old compilers are required for this to build. The compilers here
+are suggested by Amlogic, and they are 32-bit x86 binaries.
 
  > wget https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-aarch64-none-elf-4.8-2013.11_linux.tar.xz
  > wget https://releases.linaro.org/archive/13.11/components/toolchain/binaries/gcc-linaro-arm-none-eabi-4.8-2013.11_linux.tar.xz
@@ -53,7 +72,10 @@ the git tree published by the board vendor:
  > make
  > export FIPDIR=$PWD/fip
 
-Go back to mainline U-Boot source tree then :
+Once you have the binaries available (either through the prebuilt download,
+or having built the vendor u-boot yourself), you can then proceed to glue
+everything together. Go back to mainline U-Boot source tree then :
+
  > mkdir fip
 
  > cp $FIPDIR/gxl/bl2.bin fip/
@@ -100,3 +122,14 @@ and then write the image to SD with:
  > DEV=/dev/your_sd_device
  > dd if=fip/u-boot.bin.sd.bin of=$DEV conv=fsync,notrunc bs=512 skip=1 seek=1
  > dd if=fip/u-boot.bin.sd.bin of=$DEV conv=fsync,notrunc bs=1 count=444
+
+Note that Amlogic provides aml_encrypt_gxl as a 32-bit x86 binary with no
+source code. Should you prefer to avoid that, there are open source reverse
+engineered versions available:
+
+1. gxlimg <https://github.com/repk/gxlimg>, which comes with a handy
+   Makefile that automates the whole process.
+2. meson-tools <https://github.com/afaerber/meson-tools>
+
+However, these community-developed alternatives are not endorsed by or
+supported by Amlogic.