[RFC PATCH v6 01/29] target/loongarch: Add system emulation introduction

[Xiaojuan Yang <yangxiaojuan@loongson.cn>]

Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>
---
 MAINTAINERS                         |  8 +++++++
 docs/system/loongarch/loongson3.rst | 37 +++++++++++++++++++++++++++++
 target/loongarch/README             | 28 ++++++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100644 docs/system/loongarch/loongson3.rst

diff --git a/MAINTAINERS b/MAINTAINERS
index 568fb731f7..df3d738d17 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1115,6 +1115,14 @@ F: hw/net/*i82596*
 F: include/hw/net/lasi_82596.h
 F: pc-bios/hppa-firmware.img
 
+LoongArch Machines
+------------------
+Virt
+M: Xiaojuan Yang <yangxiaojuan@loongson.cn>
+M: Song Gao <gaosong@loongson.cn>
+S: Maintained
+F: docs/system/loongarch/loongson3.rst
+
 M68K Machines
 -------------
 an5206
diff --git a/docs/system/loongarch/loongson3.rst b/docs/system/loongarch/loongson3.rst
new file mode 100644
index 0000000000..367fff9d9d
--- /dev/null
+++ b/docs/system/loongarch/loongson3.rst
@@ -0,0 +1,37 @@
+loongson3 virt generic platform (``virt``)
+====================================================
+
+The ``virt`` machine use gpex host bridge, and there are some
+emulated devices on virt board, such as loongson7a RTC device,
+IOAPIC device, ACPI device and so on.
+
+Supported devices
+-----------------
+
+The ``virt`` machine supports:
+- Gpex host bridge
+- Ls7a RTC device
+- Ls7a IOAPIC device
+- Ls7a ACPI device
+- Fw_cfg device
+- PCI/PCIe devices
+- Memory device
+- CPU device. Type: Loongson-3A5000.
+
+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``.
+
+Boot options
+------------
+
+Now the ``virt`` machine can start using -bios parameter:
+
+.. code-block:: bash
+
+  $ qemu-system-loongarch64 -M virt -cpu Loongson-3A5000 -smp 2 -m 1G \
+      -display none -serial stdio \
+      -bios loongarch_bios.bin
diff --git a/target/loongarch/README b/target/loongarch/README
index 383db6cc15..de44d39561 100644
--- a/target/loongarch/README
+++ b/target/loongarch/README
@@ -71,6 +71,34 @@
       ./qemu-loongarch64  /opt/clfs/usr/bin/pwd
       ...
 
+- System emulation
+
+  Mainly emulate a virt 3A5000 board and ls7a bridge that is not exactly the same as the host.
+  3A5000 support multiple interrupt cascading while here we just emulate the extioi interrupt
+  cascading. LS7A1000 host bridge support multiple devices, such as sata, gmac, uart, rtc
+  and so on. But we just realize the rtc. Others use the qemu common devices. It does not affect
+  the general use. We also introduced the emulation of devices at docs/system/loongarch/loongson3.rst.
+
+  You can compile the binaries by youself or just get all required binaries from the github for testing.
+
+  1.Download kernel and the cross-tools.(vmlinux)
+
+      https://github.com/loongson/linux/tree/loongarch-next
+      https://github.com/loongson/build-tools/releases/latest/download/loongarch64-clfs-20211202-cross-tools.tar.xz
+
+  2.Download uefi code.(loongarch_bios.bin)
+
+      https://github.com/loongson/edk2/tree/LoongArch
+      https://github.com/loongson/edk2-platforms
+
+  3.Download the clfs-system and make a ramdisk with busybox.(ramdisk)
+
+  4.Run with command,eg:
+
+   ./build/qemu-system-loongarch64 -m 4G -smp 4 --cpu Loongson-3A5000 --machine loongson3-ls7a -kernel ./vmlinux -initrd ./ramdisk  -append "root=/dev/ram console=ttyS0,115200 rdinit=/sbin/init loglevel=8" -monitor tcp::4000,server,nowait -nographic
+
+All binaries can get from here directly:
+    git clone https://github.com/yangxiaojuan-loongson/qemu-binary
 
 - Note.
   We can get the latest LoongArch documents or LoongArch tools at https://github.com/loongson/
-- 
2.27.0