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   Simple steps used to test the SH-QSPI at U-Boot
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#0, Currently, SH-QSPI is used by lager board (Renesas ARM SoC R8A7790)
    and koelsch board (Renesas ARM SoC R8A7791). These boot from SPI ROM
    basically. Thus, U-Boot start, SH-QSPI will is operating normally.

#1, build U-Boot and load u-boot.bin

  => tftpboot 40000000 u-boot.bin
  sh_eth Waiting for PHY auto negotiation to complete.. done
  sh_eth: 100Base/Half
  Using sh_eth device
  TFTP from server 192.168.169.1; our IP address is 192.168.169.79
  Filename 'u-boot.bin'.
  Load address: 0x40000000
  Loading: ############
    2.5 MiB/s
  done
  Bytes transferred = 175364 (2ad04 hex)

#2, Commands to erase/write u-boot to flash device

  Note: This method is description of the lager board. If you want to use the
  other boards, please change the value according to each environment.

  =>  sf probe 0
  SF: Detected S25FL512S_256K with page size 512 Bytes, erase size 64 KiB, total 64 MiB
  => sf erase 80000 40000
  SF: 262144 bytes @ 0x80000 Erased: OK
  => sf write 40000000 80000 175364
  SF: 1528676 bytes @ 0x80000 Written: OK
  =>

#3, Push reset button.

  If you're written correctly and driver works properly, U-Boot starts.