initial buildroot for linux 5.15

board/orangepi/orangepi-rk3399/readme.txt

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+Orangepi Rk3399
+================
+http://www.orangepi.org/Orange%20Pi%20RK3399/
+
+Build:
+======
+  $ make orangepi_rk3399_defconfig
+  $ make
+
+Files created in output directory
+=================================
+
+output/images
+
+├── bl31.elf
+├── boot.vfat
+├── extlinux
+├── idbloader.img
+├── Image
+├── rk3399-orangepi.dtb
+├── rootfs.ext2
+├── rootfs.ext4 -> rootfs.ext2
+├── rootfs.tar
+├── sdcard.img
+├── u-boot.bin
+└── u-boot.itb
+
+Creating bootable SD card:
+==========================
+
+Simply invoke (as root)
+
+sudo dd if=output/images/sdcard.img of=/dev/sdX && sync
+
+Where X is your SD card device.
+
+Booting:
+========
+Orangepi-RK3399 by default boots from emmc. For SD card boot to
+happen, emmc should be empty. If emmc happens to have any bootable
+image then erase emmc so that bootrom will look for a proper image in SD.
+
+emmc can be erased once after booted into linux as shown in below link.
+
+https://wiki.amarulasolutions.com/bsp/setup/rockchip/rk3399_emmc.html
+
+Serial console:
+---------------
+
+Baudrate for this board is 1500000.
+
+Login:
+------
+Enter 'root' as login user, and the prompt is ready.
+
+https://wiki.amarulasolutions.com/bsp/rockchip/rk3399/orangepi.html