doc: board: amlogic: add u-boot-spl documentation

Add building and usage instructions for SPL.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Ferass El Hafidi <funderscore@postmarketos.org>
Link: https://patch.msgid.link/20251126-spl-gx-v5-10-6cbffb2451ca@postmarketos.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

doc/board/amlogic/index.rst

@@ -78,6 +78,7 @@ Boot Documentation
 
    boot-flow
    pre-generated-fip
+   spl
 
 Board Documentation
 -------------------

doc/board/amlogic/pre-generated-fip.rst

@@ -98,6 +98,13 @@ The repo also provides the following files used with GXBB boards:
 The repo also supports the open-source 'gxlimg' signing tool that can be used to sign
 U-Boot binaries for GXL/GXM/G12A/G12B/SM1 boards: https://github.com/repk/gxlimg
 
+The following binaries can be replaced with open-source implementations:
+
+- bl2.bin (GXBB and GXL only)
+- bl31.img (GXBB, GXL, AXG and G12A only)
+
+Refer to `Experimental U-Boot SPL Support`_ if you wish to replace them.
+
 Licensing
 ---------
 
@@ -129,3 +136,5 @@ clarified. The current Amlogic distribution licence is below:
     // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+.. _`Experimental U-Boot SPL Support`: spl.rst

doc/board/amlogic/spl.rst

@@ -0,0 +1,77 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Experimental U-Boot SPL Support
+===============================
+
+There's some experimental support for some Amlogic SoCs, in U-Boot SPL.  It
+replaces the proprietary bl2.bin blob used for DRAM init.  Currently Meson GX
+SoCs (GXBB, GXL) are supported.
+
+A subset of Amlogic boards have SPL enabled.  These boards have been tested and
+are known to work to an extent.
+
+
+Building Arm Trusted Firmware (TF-A)
+------------------------------------
+
+This U-Boot SPL port requires the BL31 stage of mainline Arm Trusted
+Firmware-A firmware. It provides an open source implementation of secure
+software for Armv8-A. Build it with:
+
+.. code-block:: bash
+
+    $ git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
+    $ cd trusted-firmware-a
+    $ make CROSS_COMPILE=aarch64-linux-gnu- PLAT=your_soc AML_STDPARAMS=1
+
+Replace ``your_soc`` with the SoC target you wish to build for. For GXBB it's
+``gxbb`` and for GXL it's ``gxl``.
+
+
+Building a bl30_new.bin binary
+------------------------------
+
+``bl30_new.bin`` has both ``bl30.bin`` and ``bl301.bin`` binary blobs
+bundled. The former is the proper system control processor firmware and the
+latter is a "plug-in" for board-specific DVFS/suspend-resume parameters. For
+more info you may wish to read this page: `Pre-Generated FIP File Repo`_.
+
+To build using the FIP file repo, simply issue the following commands:
+
+.. code-block:: bash
+
+    $ cd amlogic-boot-fip/your_board
+    $ make bl30_new.bin
+
+
+.. _`Pre-Generated FIP File Repo`: pre-generated-fip.rst
+
+
+U-Boot compilation
+------------------
+
+U-Boot SPL is not enabled by default, instead there are config fragments that
+can be used to enable it, with per-board configuration:
+
+- ``spl-libretech-cc-1gb.config``: 1 GB LePotato board
+- ``spl-libretech-cc-2gb.config``: 2 GB LePotato board
+- ``spl-odroid-c2.config``: ODROID-C2
+- ``spl-videostrong-kii-pro.config``: Videostrong KII Pro
+
+Pick one of them then:
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=aarch64-linux-gnu-
+    $ export BL31=path/to/tf-a/bl31.bin                 # Upstream TF-A BL31 binary
+    $ export SCP=path/to/bl30_new.bin                   # bl30_new.bin binary
+    $ make <yourboardname>_defconfig spl-<yourboardname>.config
+    $ make
+
+Write to SD:
+
+.. code-block:: bash
+
+    $ DEV=/dev/boot_device
+    $ dd if=u-boot-meson-with-spl.bin of=$DEV conv=fsync,notrunc bs=512 seek=1
+