I downloaded the source code，when I try to compile, I got this error:

  @ubuntu:~/rk356x_linux5.10$  ./build.sh kernel

  processing option: kernel

  ============Start building kernel============

  TARGET_ARCH     =arm64
  TARGET_KERNEL_CONFIG =rockchip_linux_defconfig
  TARGET_KERNEL_DTS  =rk3566-evb2-lp4x-v10-linux
  TARGET_KERNEL_CONFIG_FRAGMENT =

  ==========================================

  #
  # No change to .config
  #
    CALL    scripts/atomic/check-atomics.sh
    CALL    scripts/checksyscalls.sh
    CHK    include/generated/compile.h
    LZ4C    arch/arm64/boot/Image.lz4

  Incorrect parameters
  Usage :
        lz4 [arg] [input] [output]
  input   : a filename
        with no FILE, or when  FILE is - or stdin, read standard input
  Arguments :
   -1    : Fast compression (default)
   -9   : High compression
   -d    : decompression (default for .lz4 extension)
   -z    : force compression
   -f   : overwrite output without prompting
   -h/-H  : display help/long help and exit

  arch/arm64/boot/Makefile:31: recipe for target 'arch/arm64/boot/Image.lz4'  failed

  make[2]: *** [arch/arm64/boot/Image.lz4] Error 1
  make[2]: *** Deleting file 'arch/arm64/boot/Image.lz4'
  arch/arm64/Makefile:170: recipe for target 'Image.lz4' failed
  make[1]: *** [Image.lz4] Error 2
  make[1]: *** Waiting for unfinished jobs....
  arch/arm64/Makefile:214: recipe for target 'rk3566-evb2-lp4x-v10-linux.img'  failed
  make: *** [rk3566-evb2-lp4x-v10-linux.img] Error 2
  ERROR: Running build_kernel failed!
  ERROR: exit code 2 from line 663:
      make ARCH=$RK_ARCH $RK_KERNEL_DTS.img -j$RK_JOBS
    

Cause: The version of lz4 delivered with the compilation system is too early.
Solution: update to V1.8.3 or later.
lz4 -v            //check the compiler lz4 version
sudo cp out/host/linux-x86/bin/lz4 /usr/bin/lz   //copy lz4 from the Android source directory to override the compiler's

Camera does not work properly on board with more than 4GB of memory. After the memory is upgraded from 4GB to 8GB, open the camera APP, the terminal will output:

[  100.488782] rga_mm: RGA_MMU unsupported Memory larger than 4G!
[  100.488814] rga_mm: scheduler core[4] unsupported mm_flag[0x0]!
[  100.488821] rga_mm: rga_mm_map_buffer map dma_buf error!
[  100.488826] rga_mm: job buffer map failed!
[  100.488831] rga_mm: dst channel map job buffer failed!
[  100.488834] rga_mm: failed to map buffer
[  100.488842] rga_job: rga_job_commit: failed to map job info
[  100.488896] rga_job: request[1] task[0] job_commit failed.
[  100.488909] rga_job: rga request commit failed!
[  100.488915] rga: request[1] submit failed!

Solution: Modify the source code according to the file ddr_than-4G.patch and compile it again.

upgrade_tool is a firmware upgrade tool for Linux. Flash image requires superuser privileges.
1. Download and execute upgrade_tool first.
2. Put the firmware files and upgrade_tool in the same directory.
3. Connect the USB OTG port from the board to your PC, press the recovery button from your board, and connect the power, wait a few seconds and release the button.
4. Use the commands to flash image.
Basic Commands

  //List devices
  upgrade_tool ld   

  //Download boot
  upgrade_tool db rkxxloader.bin

  //Flash the partition table
  upgrade_tool di -p parameter.txt

  //Flash single partition image
  upgrade_tool di -k kernel.img

  //Falsh multiple partition images
  upgrade_tool di -u uboot.img -b boot.img

  //Flash the partition image with no defined abbreviation, you need to specify the partition name. 
  //Take the vendor partition as an example
  upgrade_tool di -vendor vendor.img

  //When ab partition are used, it also needs to be handled in undefined cases. 
  //Take boot_a and boot_b as example
  upgrade_tool di -boot_a boot.img -boot_b boot.img

  //Flash loader and reset
  upgrade_tool ul rkxxloader.bin  

  //Upgrade firmware and reset
  upgrade_tool uf update.img  

  //Erase device
  upgrade_tool ef rkxxloader.bin