[Buildroot] [PATCH v2] zynq: document how to use custom ps7_init files

[Matt Weber]

From: Masahiro Yamada <yamada.masahiro at socionext.com>

Since U-Boot supported SPL for Zynq boards at v2014.04 release, it
became much easier to build a system.  At that time, however, users
still needed to manually copy ps7_init.c/h to the U-Boot source tree
to generate a working SPL image because ps7_init.c/h output from
Xilinx tools are not compatible with GPL.

Later, the license problem was solved when Xilinx tools became able
to output the GPL-compatible variants (ps7_init_gpl.c/h) as well.
U-Boot v2015.07 or later includes ps7_init_gpl.c/h for major Zynq
boards so that users can build a boot image straight away.

Now Buildroot supports 3 boards (Zedboard, MicroZed, ZC706) without
any manual intervention.  This is a good thing itself, but commit
b9cd72cdbfe3 ("zynq_zc706: bump U-Boot to xilinx-v2016.2") entirely
dropped the information about custom ps7_init files.

This commit provides up-to-date guidance for how to customize the
ps7_init files.

Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
Signed-off-by: Matt Weber <matthew.weber at rockwellcollins.com>

---
v1 -> v2
 - Updated readme wording discussed in
   https://patchwork.ozlabs.org/patch/654309/

---
 board/zynq/readme.txt | 46 +++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 39 insertions(+), 7 deletions(-)

diff --git a/board/zynq/readme.txt b/board/zynq/readme.txt
index 51e28b6..364ec39 100644
--- a/board/zynq/readme.txt
+++ b/board/zynq/readme.txt
@@ -6,13 +6,6 @@ Currently, three boards are natively supported by Buildroot:
  - Avnet ZedBoard (zynq_zed_defconfig)
  - Avnet MicroZed (zynq_microzed_defconfig)
 
-The following build procedure focuses on them, but you can adjust it to your
-board even if it is not listed above.  Major Zynq-based boards are supported by
-U-Boot, and their Device Trees are merged in Linux Kernel.  If your board is the
-case, booting the kernel is a piece of cake.  All you need to do is to change:
- - Kernel Device Tree file name (BR2_LINUX_KERNEL_INTREE_DTS_NAME)
- - U-Boot board defconfig (BR2_TARGET_UBOOT_BOARD_KCONFIG)
-
 Steps to create a working system for a Zynq board:
 
 1) Configuration (do one of the following)
@@ -50,3 +43,42 @@ References:
 
  - Zedboard/Microzed information including schematics, reference designs, and
    manuals are available from http://www.zedboard.org .
+
+Support for other boards:
+
+If you want to build a system for other boards (for ex. Digilent Zybo board).
+Most major Zynq-based boards have U-Boot and Kernel support.  If your
+board happens to be supported, booting the kernel and using U-Boot
+just requires the following Buildroot updates:
+ - Kernel Device Tree file name (BR2_LINUX_KERNEL_INTREE_DTS_NAME)
+ - U-Boot board defconfig (BR2_TARGET_UBOOT_BOARD_DEFCONFIG)
+
+Custom ps7_init_gpl.c/h support:
+
+To generate a working boot.bin image, ps7_init_gpl.c/h are required in the
+U-Boot source tree.  Those files are output from the Xilinx tools, but for
+convenience, U-Boot includes the default ps7_init_gpl.c/h of popular boards.
+These files may need to be updated for any programmable logic customizations
+which impact ps7_init (clock/pin setup & mapping/AXI bridge setup/etc).
+See board/xilinx/zynq/ directory of U-Boot for natively supported ps7_init
+files.  If the ps7_init files for your board are not found in U-Boot, you need
+to add them by yourself.  (You can still override the existing ones if you want
+to customize them for your purpose.)
+
+1) Start with a defconfig supported by Buildroot (for ex. Zedboard)
+    make zynq_zed_defconfig
+
+2) make uboot-menuconfig
+    Visit the following menu and enable CONFIG_ZYNQ_CUSTOM_INIT.
+
+    ARM architecture  --->
+       [*] Use custom ps7_init provided by Xilinx tool
+
+3) Copy ps7_init_gpl.c/h generated by the Xilinx tools into
+   output/build/uboot-xilinx-<pkg version>/board/xilinx/zynq/custom_hw_platform/
+
+4) make
+
+*Notice*
+While the build will successfully complete with/without the ps7_init_gpl.*
+files, the boot.bin generated without ones will not be functional at all.
-- 
1.9.1