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Caleb is currently in integration hell (preparing to upstream) so please bare with!
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Main feature branch is [`caleb/rbx-demo-cleanup`](https://git.codelinaro.org/linaro/qcomlt/u-boot/-/tree/caleb/rbx-demo-cleanup), clone U-Boot and check out that branch.
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This is (roughly) the make wrapper I use to build U-Boot and wrap it up into the boot.img format for ABL. U-Boot includes it's own DT but we don't want to use that because it won't be seen by ABL. Instead we append the DTB to the gzipped U-Boot binary (just like with Linux) so that ABL will populate board specific bits like the memory node. This is in contrast to current dragonboard documentation in U-Boot which did rely on hardcoding everything.
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Drop these somewhere and source them.
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```sh
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KERNEL_OUTDIR=.output
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# Make wrapper
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mu() {
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make O=$KERNEL_OUTDIR CROSS_COMPILE=aarch64-linux-gnu- -j"$(nproc --all)" $@
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}
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# Make and generate boot image wrapper
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budt() {
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mu || return 1
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rm "$KERNEL_OUTDIR"/u-boot-nodtb.bin.gz 2>/dev/null || true
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gzip "$KERNEL_OUTDIR"/u-boot-nodtb.bin
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rm -f /tmp/dt.dtb
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for DT in "$@"; do
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cat "$KERNEL_OUTDIR"/arch/arm/dts/"$DT".dtb >> /tmp/dt.dtb
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done
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mkbootimg --base '0x00000000' \
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--kernel_offset '0x00008000' \
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--ramdisk_offset '0x01000000' \
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--tags_offset '0x00000100' \
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--pagesize '4096' \
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--kernel /tmp/kernel-dtb -o '/tmp/u-boot.img'
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}
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```
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Now we can build U-Boot and boot it.
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```sh
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mu rbx_defconfig
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budt dragonboard845c
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fastboot boot /tmp/u-boot.img
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```
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This will work on RB1/2/3/5 with their respective DTBs specified. From my testing, RB3 and 5 have "good enough" DTB selection in ABL so that a single image can work on both, demonstrated below by appending both DTBs.
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```sh
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budt rb1
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budt rb2
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budt dragonboard845c rb5
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```
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## Configuring
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The default environment will scan UFS, sdcard, and USB, it will boot the first EFI bootloader it can find (a binary at patch `/EFI/Boot/bootaa64.efi` on the partition). This uses a feature called [standard boot](https://u-boot.readthedocs.io/en/latest/develop/bootstd.html). To boot a boot.img file it would be necessary to enable support for decoding Android boot images in U-Boot (some config option), and then adding a "bootmeth" which would discover the boot.img file at some well known path, unpack it and boot it. (see `boot/bootmeth_efi.c` as an example).
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The environment can be adjusted in `include/configs/qcom-common.h`.
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## Debugging
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If necessary, open `configs/rbx_defconfig` and at the bottom enable `CONFIG_DEBUG_UART` and ensure that `CONFIG_DEBUG_UART_CLOCK=7372800` is set. The loglevel can also be adjusted, and U-Boot will print logs pre-relocation + device discovery logs. This can be a little verbose so a good alternative is to add `#define LOG_DEBUG` to the top of the files you want to debug. |
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\ No newline at end of file |
