buildroot: Simplify BeaglePlay boot chain approach

Instead of having Buildroot build the full TI K3 boot chain (ATF,
OP-TEE, ti-k3-boot-firmware, binman), which requires complex
configuration and TI's downstream U-Boot fork, simplify by:

- Providing both tiboot3.bin and tispl.bin as pre-built binaries
- Only building u-boot.img through Buildroot
- Using BINMAN_ALLOW_MISSING=1 custom make option to let U-Boot
  build complete without the first-stage firmware blobs

This approach is more reliable for students and avoids dependency
on TI-specific firmware that may change between releases. The lab
explains what each binary does and points to the Embedded Linux
course for those who want to build the full chain.

Also fixes: trailing dots on commands, tispl.bin_unsigned references,
and adds tispl.bin to lab-data.

Author: kostyakozko

common/beagleplay-sdcard-preparation.tex

@@ -8,7 +8,7 @@ \section{Prepare the SD card}
   the requirements of the AM62x SoC so that the ROM code can find
   the bootloader in this partition. It should be a FAT32 partition.
   We will store the bootloader files (\code{tiboot3.bin},
-  \code{tispl.bin} and \code{u-boot.img}), the kernel image
+  \code{tispl.bin_unsigned} and \code{u-boot.img}), the kernel image
   (\code{Image}) and the Device Tree
   (\code{k3-am625-beagleplay.dtb}).
 
@@ -60,10 +60,10 @@ \section{Prepare the SD card}
   \end{itemize}
 
 \item Format the first partition as a {\em FAT32} filesystem:\\
-  \code{sudo mkfs.vfat -F 32 -n boot /dev/mmcblk0p1}.
+  \code{sudo mkfs.vfat -F 32 -n boot /dev/mmcblk0p1}
 
 \item Format the second partition as an {\em ext4} filesystem:\\
-  \code{sudo mkfs.ext4 -L rootfs -E nodiscard /dev/mmcblk0p2}.
+  \code{sudo mkfs.ext4 -L rootfs -E nodiscard /dev/mmcblk0p2}
 
 \begin{itemize}
 \item \code{-L} assigns a volume name to the partition

lab-data/buildroot-beagleplay/buildroot-basic/data/tispl.bin

@@ -192,68 +192,41 @@ \section{Configuring Buildroot}
     \code{am62x_beagleplay_a53_defconfig}. So enter
     \code{am62x_beagleplay_a53} as the \code{Board defconfig}.
 
-  \item U-Boot on AM62x produces two main images for the A53 boot
-    stage: \code{tispl.bin} (containing the U-Boot SPL and TF-A) and
-    \code{u-boot.img} (the full U-Boot). Select \code{u-boot.img} as
-    the \code{U-Boot binary format}, and enable \code{Install U-Boot
-      SPL binary image} with \code{tispl.bin\_unsigned} as the
-    \code{U-Boot SPL/TPL binary image name(s)}.
+  \item Select \code{u-boot.img} as the \code{U-Boot binary format}.
+    We only need Buildroot to produce \code{u-boot.img} (the second
+    stage bootloader). The first stage bootloaders are provided
+    pre-built (see note below).
 
-  \end{itemize}
-
-\item Still in the \code{Bootloaders} menu, enable \code{ARM Trusted
-    Firmware (ATF)}. The U-Boot build for AM62x needs the TF-A BL31
-  binary. Configure it with:
+  \item In \code{Custom make options}, enter
+    \code{BINMAN_ALLOW_MISSING=1}. This allows the U-Boot build to
+    complete even though we are not building the first-stage boot
+    images (which require additional firmware blobs).
 
-  \begin{itemize}
-  \item \code{ATF Version}: use the default or a recent version
-  \item \code{ATF platform}: enter \code{k3}
-  \item \code{ATF target board}: enter \code{lite}
-  \end{itemize}
-
-\item Still in the \code{Bootloaders} menu, enable
-  \code{optee_os}. The AM62x U-Boot expects an OP-TEE binary.
-  Configure it with:
-
-  \begin{itemize}
-  \item \code{Target platform (mandatory)}: enter \code{k3}
-  \item \code{Target platform flavor (optional)}: enter \code{am62x}
-  \end{itemize}
-
-\item Still in the \code{Bootloaders} menu, enable
-  \code{ti-k3-boot-firmware}. This provides the TI Device Manager
-  firmware that runs on the Cortex-M4F core.
-
-\item Now go back to the \code{U-Boot} options in the
-  \code{Bootloaders} menu. You should now see additional options
-  that appeared after enabling ATF and OP-TEE:
-
-  \begin{itemize}
-  \item Enable \code{U-Boot use binman}. This is required for
-    AM62x, as U-Boot uses binman to assemble the final boot images.
-  \item Enable \code{U-Boot needs ATF BL31} and select
-    \code{bl31.bin} as the \code{U-Boot ATF BL31 format}.
-  \item Enable \code{U-Boot needs OPTEE TEE} and select
-    \code{tee.bin} as the format if given a choice.
   \end{itemize}
 
 \item {\bf Note:} The AM62x SoC has a complex multi-stage boot
     process involving multiple processor cores. Before the Cortex-A53
     cores can run U-Boot, a Cortex-R5F core must first initialize the
     SoC (configure the DDR memory, load TI Foundational Security
-    firmware, etc.). This first-stage binary is called
-    \code{tiboot3.bin} and is a combination of the R5 U-Boot SPL and
-    TI firmware, packaged together using TI's \code{k3-image-gen}
-    tool.
-
-    Building \code{tiboot3.bin} requires a separate 32-bit ARM
-    toolchain (\code{arm-none-eabi-}), the TI firmware from
-    \code{ti-linux-firmware}, and the \code{k3-image-gen} tool. Since
-    this is outside the scope of Buildroot, we provide a pre-built
-    \code{tiboot3.bin} in the lab data directory at
+    firmware, etc.). The first-stage boot chain consists of:
+
+    \begin{itemize}
+    \item \code{tiboot3.bin}: the R5 U-Boot SPL combined with TI
+      system firmware, which initializes DDR and starts the A53 cores.
+    \item \code{tispl.bin}: a FIT image containing the A53 U-Boot SPL,
+      ARM Trusted Firmware (TF-A), OP-TEE, and the TI Device Manager
+      firmware. This is loaded by \code{tiboot3.bin} and handles the
+      secure boot chain before loading \code{u-boot.img}.
+    \end{itemize}
+
+    Building these first-stage images requires TI's downstream U-Boot
+    fork, a separate 32-bit ARM toolchain (\code{arm-none-eabi-}), and
+    TI firmware from \code{ti-linux-firmware}. Since this is outside
+    the scope of Buildroot, we provide pre-built \code{tiboot3.bin}
+    and \code{tispl.bin} in the lab data directory at
     \code{$HOME/__SESSION_NAME__-labs/buildroot-basic/data/}.
 
-    If you want to learn how to build it yourself, refer to the
+    If you want to learn how to build them yourself, refer to the
     Bootlin {\em Embedded Linux} training course, which covers the
     full AM62x boot chain in detail.
 
@@ -290,20 +263,21 @@ \section{Flash the system}
 
 \begin{itemize}
 
-\item Copy the pre-built \code{tiboot3.bin} from the lab data directory
+\item Copy the pre-built \code{tiboot3.bin} and \code{tispl.bin} from
+  the lab data directory
   \code{$HOME/__SESSION_NAME__-labs/buildroot-basic/data/} to the
   \code{boot} partition of the SD card.
 
-\item Copy \code{tispl.bin} and \code{u-boot.img} from
-  \code{output/images/} to the \code{boot} partition of the SD card.
+\item Copy \code{u-boot.img} from \code{output/images/} to the
+  \code{boot} partition of the SD card.
 
 \item Copy the \code{Image} and \code{k3-am625-beagleplay.dtb} files
   from \code{output/images/} to the \code{boot} partition of the SD
   card.
 
 \item Extract the \code{rootfs.tar} file to the \code{rootfs}
   partition of the SD card, using:\\
-  \inlinebash{sudo tar -C /media/$USER/rootfs/ -xf output/images/rootfs.tar}.
+  \inlinebash{sudo tar -C /media/$USER/rootfs/ -xf output/images/rootfs.tar}
 
 \item Create a file named \code{extlinux/extlinux.conf} in the
   \code{boot} partition. This file should contain the following lines: