[PATCH v4 4/5] doc: board/qualcomm: document iq9 building and flashing

[Varadarajan Narayanan]

The steps are similar to other boards. Minor difference in
the way environment variables are stored.

Signed-off-by: Varadarajan Narayanan <quic_varada at quicinc.com>
---
 doc/board/qualcomm/iq9.rst | 62 ++++++++++++++++++++++++++++++++++++++
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+.. SPDX-License-Identifier: GPL-2.0+
+.. sectionauthor:: Caleb Connolly <quic_varada at quicinc.com>
+
+Qualcomm Dragonwing IQ9 Series
+==============================
+
+The Dragonwing IQ9 Series delivers unmatched on-device AI performance for the
+most demanding industrial applications, as well as available built-in safety
+features and design flexibility for high-compute, powerefficient performance
+capable of handling heavy workloads in extreme environments. More information
+can be found on `Qualcomm's product page`_.
+
+U-Boot can be used as a replacement for Qualcomm's original EDK2 bootloader by
+flashing it directly to the uefi_a (or _b) partition.
+
+.. _Qualcomm's product page: https://docs.qualcomm.com/bundle/publicresource/87-83840-1_REV_A_Qualcomm_IQ9_Series_Product_Brief.pdf
+
+Installation
+------------
+First, setup ``CROSS_COMPILE`` for aarch64. Then, build U-Boot for ``qcm6490``::
+
+  $ export CROSS_COMPILE=<aarch64 toolchain prefix>
+  $ make qcs9100_defconfig
+  $ make -j8
+
+This will build ``u-boot.elf`` in the configured output directory.
+
+Although the RB3 Gen 2 does not have secure boot set up by default,
+the firmware still expects firmware ELF images to be "signed". The signature
+does not provide any security in this case, but it provides the firmware with
+some required metadata.
+
+To "sign" ``u-boot.elf`` you can use e.g. `qtestsign`_::
+
+  $ qtestsign -v6 aboot -o u-boot.mbn u-boot.elf
+
+Then install the resulting ``u-boot.mbn`` to the ``uefi_a`` partition
+on your device with ``fastboot flash uefi_a u-boot.mbn``.
+
+U-Boot should be running after a reboot (``fastboot reboot``).
+
+Note that fastboot is not yet supported in U-Boot on this board, as a result,
+to flash back the original firmware, or new versoins of the U-Boot, EDL mode
+must be used. This can be accessed by pressing the EDL mode button as described
+in the Qualcomm Linux documentation. A tool like bkerler's `edl`_ can be used
+for flashing with the firehose loader binary appropriate for the board.
+
+Environment Variables
+---------------------
+* The environment can be stored and retrieved directly from UFS partitions.
+
+* Environment variable partition details
+
+	UUID: 71cb9cd0-acf1-b6cb-ad91-be9572fe11a9
+
+* Relevant config options
+
+	CONFIG_ENV_IS_IN_SCSI
+	CONFIG_SCSI_ENV_PART_UUID
+
+.. _qtestsign: https://github.com/msm8916-mainline/qtestsign
+.. _edl: https://github.com/bkerler/edl
-- 
2.34.1