$ litex/litex/boards/targets/versa_ecp5.py --gateware-toolchain trellis --yosys-nowidelut --csr-csv ./csr_ecp5versa.csv         --with-ethernet --sys-clk-freq=60e6 --cpu-type rocket --cpu-variant linux

Traceback (most recent call last):
  File "litex/litex/boards/targets/versa_ecp5.py", line 151, in <module>
    main()
  File "litex/litex/boards/targets/versa_ecp5.py", line 146, in main
    soc = cls(toolchain=args.toolchain, sys_clk_freq=int(float(args.sys_clk_freq)), **soc_sdram_argdict(args))
  File "litex/litex/boards/targets/versa_ecp5.py", line 112, in __init__
    BaseSoC.__init__(self, toolchain=toolchain, integrated_rom_size=0x10000, **kwargs)
  File "litex/litex/boards/targets/versa_ecp5.py", line 85, in __init__
    **kwargs)
  File "/home/somlo/LITEX/litex/litex/soc/integration/soc_sdram.py", line 29, in __init__
    SoCCore.__init__(self, platform, clk_freq, **kwargs)
  File "/home/somlo/LITEX/litex/litex/soc/integration/soc_core.py", line 237, in __init__
    self.submodules.uart_phy = uart.UARTPHY(platform.request(uart_name), clk_freq, uart_baudrate)
  File "/home/somlo/LITEX/litex/litex/build/generic_platform.py", line 274, in request
    return self.constraint_manager.request(*args, **kwargs)
  File "/home/somlo/LITEX/litex/litex/build/generic_platform.py", line 182, in request
    resource = _lookup(self.available, name, number)
  File "/home/somlo/LITEX/litex/litex/build/generic_platform.py", line 89, in _lookup
    raise ConstraintError("Resource not found: {}:{}".format(name, number))
litex.build.generic_platform.ConstraintError: Resource not found: "serial":None