docs/system/loongarch: Update the LoongArch document

1. Add some information about how to boot the LoongArch virt
machine by uefi bios and linux kernel and how to access the
source code or binary file.
2. Move the explanation of LoongArch system emulation in the
target/loongarch/README to docs/system/loongarch/loongson3.rst

Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20220812091957.3338126-1-yangxiaojuan@loongson.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

docs/system/loongarch/loongson3.rst

@@ -15,27 +15,115 @@ The ``virt`` machine supports:
 - Gpex host bridge
 - Ls7a RTC device
 - Ls7a IOAPIC device
-- Ls7a ACPI device
+- ACPI GED device
 - Fw_cfg device
 - PCI/PCIe devices
 - Memory device
-- CPU device. Type: Loongson-3A5000.
+- CPU device. Type: la464-loongarch-cpu.
 
 CPU and machine Type
 --------------------
 
 The ``qemu-system-loongarch64`` provides emulation for virt
 machine. You can specify the machine type ``virt`` and
-cpu type ``Loongson-3A5000``.
+cpu type ``la464-loongarch-cpu``.
 
 Boot options
 ------------
 
-Now the ``virt`` machine can run test program in ELF format and the
-method of compiling is in target/loongarch/README.
+We can boot the LoongArch virt machine by specifying the uefi bios,
+initrd, and linux kernel. And those source codes and binary files
+can be accessed by following steps.
+
+(1) booting command:
 
 .. code-block:: bash
 
-  $ qemu-system-loongarch64 -machine virt -m 4G -cpu Loongson-3A5000 \
-      -smp 1 -kernel hello -monitor none -display none \
-      -chardev file,path=hello.out,id=output -serial chardev:output
+  $ qemu-system-loongarch64 -machine virt -m 4G -cpu la464-loongarch-cpu \
+      -smp 1 -bios QEMU_EFI.fd -kernel vmlinuz.efi -initrd initrd.img \
+      -append "root=/dev/ram rdinit=/sbin/init consol e=ttyS0,115200" \
+      --nographic
+
+Note: The running speed may be a little slow, as the performance of our
+qemu and uefi bios is not perfect, and it is being fixed.
+
+(2) cross compiler tools:
+
+.. code-block:: bash
+
+  wget https://github.com/loongson/build-tools/releases/download/ \
+  2022.05.29/loongarch64-clfs-5.0-cross-tools-gcc-full.tar.xz
+
+  tar -vxf loongarch64-clfs-5.0-cross-tools-gcc-full.tar.xz
+
+(3) qemu compile configure option:
+
+.. code-block:: bash
+
+  ./configure --disable-rdma --disable-pvrdma --prefix=usr \
+              --target-list="loongarch64-softmmu" \
+              --disable-libiscsi --disable-libnfs --disable-libpmem \
+              --disable-glusterfs --enable-libusb --enable-usb-redir \
+              --disable-opengl --disable-xen --enable-spice \
+              --enable-debug --disable-capstone --disable-kvm \
+              --enable-profiler
+  make
+
+(4) uefi bios source code and compile method:
+
+.. code-block:: bash
+
+  git clone https://github.com/loongson/edk2-LoongarchVirt.git
+
+  cd edk2-LoongarchVirt
+
+  git submodule update --init
+
+  export PATH=$YOUR_COMPILER_PATH/bin:$PATH
+
+  export WORKSPACE=`pwd`
+
+  export PACKAGES_PATH=$WORKSPACE/edk2-LoongarchVirt
+
+  export GCC5_LOONGARCH64_PREFIX=loongarch64-unknown-linux-gnu-
+
+  edk2-LoongarchVirt/edksetup.sh
+
+  make -C edk2-LoongarchVirt/BaseTools
+
+  build --buildtarget=DEBUG --tagname=GCC5 --arch=LOONGARCH64  --platform=OvmfPkg/LoongArchQemu/Loongson.dsc
+
+  build --buildtarget=RELEASE --tagname=GCC5 --arch=LOONGARCH64  --platform=OvmfPkg/LoongArchQemu/Loongson.dsc
+
+The efi binary file path:
+
+  Build/LoongArchQemu/DEBUG_GCC5/FV/QEMU_EFI.fd
+
+  Build/LoongArchQemu/RELEASE_GCC5/FV/QEMU_EFI.fd
+
+(5) linux kernel source code and compile method:
+
+.. code-block:: bash
+
+  git clone https://github.com/loongson/linux.git
+
+  export PATH=$YOUR_COMPILER_PATH/bin:$PATH
+
+  export LD_LIBRARY_PATH=$YOUR_COMPILER_PATH/lib:$LD_LIBRARY_PATH
+
+  export LD_LIBRARY_PATH=$YOUR_COMPILER_PATH/loongarch64-unknown-linux-gnu/lib/:$LD_LIBRARY_PATH
+
+  make ARCH=loongarch CROSS_COMPILE=loongarch64-unknown-linux-gnu- loongson3_defconfig
+
+  make ARCH=loongarch CROSS_COMPILE=loongarch64-unknown-linux-gnu-
+
+  make ARCH=loongarch CROSS_COMPILE=loongarch64-unknown-linux-gnu- install
+
+  make ARCH=loongarch CROSS_COMPILE=loongarch64-unknown-linux-gnu- modules_install
+
+Note: The branch of linux source code is loongarch-next.
+
+(6) initrd file:
+
+  You can use busybox tool and the linux modules to make a initrd file. Or you can access the
+  binary files: https://github.com/yangxiaojuan-loongson/qemu-binary