[PATCH v2] colibri_imx7: add readme.rst doc

[Igor Opaniuk]

From: Igor Opaniuk <igor.opaniuk at toradex.com>

Add initial readme.rst file which provides all needed information
for obtaining a workable image ready for flashing
for both eMMC/NAND versions of Colibri iMX7.

Signed-off-by: Igor Opaniuk <igor.opaniuk at toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov at toradex.com>
---

v2:
- Converted to reStructuredText format [Bin Meng]

 board/toradex/colibri_imx7/readme.rst | 128 ++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 board/toradex/colibri_imx7/readme.rst

diff --git a/board/toradex/colibri_imx7/readme.rst b/board/toradex/colibri_imx7/readme.rst
new file mode 100644
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+++ b/board/toradex/colibri_imx7/readme.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for Colibri iMX7
+=======================
+
+Quick Start
+-----------
+
+- Build U-Boot
+- NAND IMX image adjustments before flashing
+- Flashing manually U-Boot to eMMC
+- Flashing manually U-Boot to NAND
+- Using ``update_uboot`` script
+
+Build U-Boot
+------------
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=arm-linux-gnueabi-
+    $ export ARCH=arm
+    $ make colibri_imx7_emmc_defconfig # For NAND: colibri_imx7_defconfig
+    $ make
+
+After build succeeds, you will obtain final ``u-boot-dtb.imx`` IMX specific
+image, ready for flashing (but check next section for additional
+adjustments for NAND).
+
+Final IMX program image includes (section ``6.6.7`` from `IMX7DRM
+<https://www.nxp.com/webapp/Download?colCode=IMX7DRM>`_):
+
+* **Image vector table** (IVT) for BootROM
+* **Boot data** -indicates the program image location, program image size
+  in bytes, and the plugin flag.
+* **Device configuration data**
+* **User image**: U-Boot image (``u-boot-dtb.bin``)
+
+
+NAND IMX image adjustments prior to flashing
+--------------------------------------------
+
+1. U-Boot for both Colibri iMX7 NAND and eMMC versions
+is built with HABv4 support (`AN4581.pdf
+<https://www.nxp.com/docs/en/application-note/AN4581.pdf>`_)
+enabled by default, which requires to generate a proper
+Command Sequence File (CSF) by srktool from NXP (not included in the
+U-Boot tree, check additional details in introduction_habv4.txt)
+and concatenate it to the final ``u-boot-dtb.imx``.
+
+2. In case if you don't want to generate a proper ``CSF`` (for any reason),
+you still need to pad the IMX image so i has the same size as specified in
+in **Boot Data** section of IMX image.
+To obtain this value, run:
+
+.. code-block:: bash
+
+    $ od -X -N 0x30 u-boot-dtb.imx
+    0000000    402000d1 87800000 00000000 877ff42c
+    0000020    877ff420 877ff400 878a5000 00000000
+                        ^^^^^^^^
+    0000040    877ff000 000a8060 00000000 40b401d2
+               ^^^^^^^^ ^^^^^^^^
+
+Where:
+
+* ``877ff400`` - IVT self address
+* ``877ff000`` - Program image address
+* ``000a8060`` - Program image size
+
+To calculate the padding:
+
+* IVT offset = ``0x877ff400`` - ``0x877ff000`` = ``0x400``
+* Program image size = ``0xa8060`` - ``0x400`` = ``0xa7c60``
+
+and then pad the image:
+
+.. code-block:: bash
+
+    $ objcopy -I binary -O binary --pad-to 0xa7c60 --gap-fill=0x00 \
+        u-boot-dtb.imx u-boot-dtb.imx.zero-padded
+
+3. Also, according to requirement from ``6.6.7.1``, the final image
+should have ``0x400`` offset for initial IVT table.
+
+For eMMC setup we handle this by flashing it to ``0x400``, howewer
+for NAND setup we adjust the image prior to flashing, adding padding in the
+beginning of the image.
+
+.. code-block:: bash
+
+    $ dd if=u-boot-dtb.imx.zero-padded of=u-boot-dtb.imx.ready bs=1024 seek=1
+
+Flash U-Boot IMX image to eMMC
+------------------------------
+
+Flash the ``u-boot-dtb.imx`` binary to the primary eMMC hardware
+boot area partition:
+
+.. code-block:: bash
+
+
+    => load mmc 1:1 $loadaddr u-boot-dtb.imx
+    => setexpr blkcnt ${filesize} + 0x1ff && setexpr blkcnt ${blkcnt} / 0x200
+    => mmc dev 0 1
+    => mmc write ${loadaddr} 0x2 ${blkcnt}
+
+Flash U-boot IMX image to NAND
+------------------------------
+
+.. code-block:: bash
+
+    => load mmc 1:1 $loadaddr u-boot-dtb.imx.ready
+    => nand erase.part u-boot1
+    => nand write ${loadaddr} u-boot1 ${filesize}
+    => nand erase.part u-boot2
+    => nand write ${loadaddr} u-boot2 ${filesize}
+
+Using update_uboot script
+-------------------------
+
+You can also usb U-boot env update_uboot script,
+which wraps all eMMC/NAND specific command invocation:
+
+.. code-block:: bash
+
+    => load mmc 1:1 $loadaddr u-boot-dtb.imx
+    => run update_uboot
+
-- 
2.17.1