riscv/virt: add virt_nsh with docs

This adds `rv-virt:virt_nsh` config w/ docs for using virtio serial
as NuttX console.

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>

Documentation/platforms/risc-v/qemu-rv/boards/rv-virt/index.rst

@@ -359,6 +359,26 @@ flats64
 Similar to the `nsh`_ configuration, but running in S-mode.
 This configuration is used for 64-bit RISC-V
 
+virt_nsh
+--------
+
+Similar to `nsh`_ configuration, but uses virtio serial device as console.
+Use it below with QEMU::
+
+    $ qemu-system-riscv32 -M virt,aclint=on -nographic \
+    -chardev socket,id=aux,path=/tmp/aux,server=on,wait=on \
+    -device virtio-serial-device,bus=virtio-mmio-bus.0 \
+    -device virtconsole,chardev=aux \
+    -bios nuttx
+
+Then from another terminal, use below command to access the console::
+
+    $ socat UNIX-CLIENT:/tmp/aux -
+
+We can finish the session with ``quit`` command in NSH session.
+
+Note the above command line uses UNIX domain socket so please change the socket parameters on hosts without UNIX domain socket.
+
 RISC-V GDB Debugging
 ====================
 

boards/risc-v/qemu-rv/rv-virt/configs/virt_nsh/defconfig

@@ -0,0 +1,66 @@
+#
+# This file is autogenerated: PLEASE DO NOT EDIT IT.
+#
+# You can use "make menuconfig" to make any modifications to the installed .config file.
+# You can then do "make savedefconfig" to generate a new defconfig file that includes your
+# modifications.
+#
+# CONFIG_DISABLE_OS_API is not set
+# CONFIG_NSH_DISABLE_LOSMART is not set
+CONFIG_ARCH="risc-v"
+CONFIG_ARCH_BOARD="rv-virt"
+CONFIG_ARCH_BOARD_QEMU_RV_VIRT=y
+CONFIG_ARCH_CHIP="qemu-rv"
+CONFIG_ARCH_CHIP_QEMU_RV32=y
+CONFIG_ARCH_CHIP_QEMU_RV=y
+CONFIG_ARCH_CHIP_QEMU_RV_ISA_A=y
+CONFIG_ARCH_CHIP_QEMU_RV_ISA_C=y
+CONFIG_ARCH_CHIP_QEMU_RV_ISA_M=y
+CONFIG_ARCH_INTERRUPTSTACK=2048
+CONFIG_ARCH_RISCV=y
+CONFIG_ARCH_STACKDUMP=y
+CONFIG_BOARDCTL_POWEROFF=y
+CONFIG_BOARD_EARLY_INITIALIZE=y
+CONFIG_BOARD_LOOPSPERMSEC=6366
+CONFIG_BUILTIN=y
+CONFIG_DEBUG_ASSERTIONS=y
+CONFIG_DEBUG_FEATURES=y
+CONFIG_DEBUG_FULLOPT=y
+CONFIG_DEBUG_SYMBOLS=y
+CONFIG_DEV_SIMPLE_ADDRENV=y
+CONFIG_DEV_ZERO=y
+CONFIG_DRIVERS_VIRTIO=y
+CONFIG_DRIVERS_VIRTIO_MMIO=y
+CONFIG_DRIVERS_VIRTIO_SERIAL=y
+CONFIG_DRIVERS_VIRTIO_SERIAL_CONSOLE=y
+CONFIG_ELF=y
+CONFIG_EXAMPLES_HELLO=y
+CONFIG_FS_HOSTFS=y
+CONFIG_FS_PROCFS=y
+CONFIG_IDLETHREAD_STACKSIZE=2048
+CONFIG_INIT_ENTRYPOINT="nsh_main"
+CONFIG_LIBC_ENVPATH=y
+CONFIG_LIBC_EXECFUNCS=y
+CONFIG_LIBC_PERROR_STDOUT=y
+CONFIG_LIBC_STRERROR=y
+CONFIG_LIBM=y
+CONFIG_NFILE_DESCRIPTORS_PER_BLOCK=6
+CONFIG_NSH_ARCHINIT=y
+CONFIG_NSH_BUILTIN_APPS=y
+CONFIG_NSH_FILEIOSIZE=512
+CONFIG_NSH_READLINE=y
+CONFIG_PATH_INITIAL="/system/bin"
+CONFIG_RAM_SIZE=16777216
+CONFIG_RAM_START=0x80000000
+CONFIG_READLINE_CMD_HISTORY=y
+CONFIG_RISCV_SEMIHOSTING_HOSTFS=y
+CONFIG_RR_INTERVAL=200
+CONFIG_SCHED_WAITPID=y
+CONFIG_STACK_COLORATION=y
+CONFIG_START_MONTH=12
+CONFIG_START_YEAR=2021
+CONFIG_SYMTAB_ORDEREDBYNAME=y
+CONFIG_SYSTEM_NSH=y
+CONFIG_TESTING_GETPRIME=y
+CONFIG_TESTING_OSTEST=y
+CONFIG_USEC_PER_TICK=1000