docs/system: Add entry for LoongArch system

Add index entry for LoongArch system and do some small modification
with  LoongArch document with rst syntax.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>

docs/system/loongarch/virt.rst

@@ -12,14 +12,15 @@ Supported devices
 -----------------
 
 The ``virt`` machine supports:
-- Gpex host bridge
+
-- Ls7a RTC device
+* Gpex host bridge
-- Ls7a IOAPIC device
+* Ls7a RTC device
-- ACPI GED device
+* Ls7a IOAPIC device
-- Fw_cfg device
+* ACPI GED device
-- PCI/PCIe devices
+* Fw_cfg device
-- Memory device
+* PCI/PCIe devices
-- CPU device. Type: la464.
+* Memory device
+* CPU device. Type: la464.
 
 CPU and machine Type
 --------------------
@@ -39,13 +40,7 @@ can be accessed by following steps.
 
 .. code-block:: bash
 
-  ./configure --disable-rdma --prefix=/usr \
+  ./configure --target-list="loongarch64-softmmu"
-              --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 -j8
 
 (2) Set cross tools:
@@ -53,9 +48,7 @@ can be accessed by following steps.
 .. code-block:: bash
 
   wget https://github.com/loongson/build-tools/releases/download/2022.09.06/loongarch64-clfs-6.3-cross-tools-gcc-glibc.tar.xz
-
   tar -vxf loongarch64-clfs-6.3-cross-tools-gcc-glibc.tar.xz  -C /opt
-
   export PATH=/opt/cross-tools/bin:$PATH
   export LD_LIBRARY_PATH=/opt/cross-tools/lib:$LD_LIBRARY_PATH
   export LD_LIBRARY_PATH=/opt/cross-tools/loongarch64-unknown-linux-gnu/lib/:$LD_LIBRARY_PATH
@@ -74,13 +67,9 @@ Note: To build the release version of the bios,  set --buildtarget=RELEASE,
 .. code-block:: bash
 
   git clone https://github.com/loongson/linux.git
-
   cd linux
-
   git checkout loongarch-next
-
   make ARCH=loongarch CROSS_COMPILE=loongarch64-unknown-linux-gnu- loongson3_defconfig
-
   make ARCH=loongarch CROSS_COMPILE=loongarch64-unknown-linux-gnu- -j32
 
 Note: The branch of linux source code is loongarch-next.

docs/system/target-loongarch.rst

@@ -0,0 +1,19 @@
+.. _LoongArch-System-emulator:
+
+LoongArch System emulator
+-------------------------
+
+QEMU can emulate loongArch 64 bit systems via the
+``qemu-system-loongarch64`` binary. Only one machine type ``virt`` is
+supported.
+
+When using KVM as accelerator, QEMU can emulate la464 cpu model. And when
+using the default cpu model with TCG as accelerator, QEMU will emulate a
+subset of la464 cpu features that should be enough to run distributions
+built for the la464.
+
+Board-specific documentation
+============================
+
+.. toctree::
+   loongarch/virt

docs/system/targets.rst

@@ -18,6 +18,7 @@ Contents:
 
    target-arm
    target-avr
+   target-loongarch
    target-m68k
    target-mips
    target-ppc