docs/system: openrisc: Add OpenRISC documentation

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Stafford Horne <shorne@gmail.com>

docs/system/openrisc/cpu-features.rst

@@ -0,0 +1,15 @@
+CPU Features
+============
+
+The QEMU emulation of the OpenRISC architecture provides following built in
+features.
+
+- Shadow GPRs
+- MMU TLB with 128 entries, 1 way
+- Power Management (PM)
+- Programmable Interrupt Controller (PIC)
+- Tick Timer
+
+These features are on by default and the presence can be confirmed by checking
+the contents of the Unit Presence Register (``UPR``) and CPU Configuration
+Register (``CPUCFGR``).

docs/system/openrisc/emulation.rst

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+OpenRISC 1000 CPU architecture support
+======================================
+
+QEMU's TCG emulation includes support for the OpenRISC or1200 implementation of
+the OpenRISC 1000 cpu architecture.
+
+The or1200 cpu also has support for the following instruction subsets:
+
+- ORBIS32 (OpenRISC Basic Instruction Set)
+- ORFPX32 (OpenRISC Floating-Point eXtension)
+
+In addition to the instruction subsets the QEMU TCG emulation also has support
+for most Class II (optional) instructions.
+
+For information on all OpenRISC instructions please refer to the latest
+architecture manual available on the OpenRISC website in the
+`OpenRISC Architecture <https://openrisc.io/architecture>`_ section.

docs/system/openrisc/or1k-sim.rst

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+Or1ksim board
+=============
+
+The QEMU Or1ksim machine emulates the standard OpenRISC board simulator which is
+also the standard SoC configuration.
+
+Supported devices
+-----------------
+
+ * 16550A UART
+ * ETHOC Ethernet controller
+ * SMP (OpenRISC multicore using ompic)
+
+Boot options
+------------
+
+The Or1ksim machine can be started using the ``-kernel`` and ``-initrd`` options
+to load a Linux kernel and optional disk image.
+
+.. code-block:: bash
+
+  $ qemu-system-or1k -cpu or1220 -M or1k-sim -nographic \
+        -kernel vmlinux \
+        -initrd initramfs.cpio.gz \
+        -m 128
+
+Linux guest kernel configuration
+""""""""""""""""""""""""""""""""
+
+The 'or1ksim_defconfig' for Linux openrisc kernels includes the right
+drivers for the or1ksim machine.  If you would like to run an SMP system
+choose the 'simple_smp_defconfig' config.
+
+Hardware configuration information
+""""""""""""""""""""""""""""""""""
+
+The ``or1k-sim`` board automatically generates a device tree blob ("dtb")
+which it passes to the guest. This provides information about the
+addresses, interrupt lines and other configuration of the various devices
+in the system.
+
+The location of the DTB will be passed in register ``r3`` to the guest operating
+system.

docs/system/openrisc/virt.rst

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+'virt' generic virtual platform
+===============================
+
+The ``virt`` board is a platform which does not correspond to any
+real hardware; it is designed for use in virtual machines.
+It is the recommended board type if you simply want to run
+a guest such as Linux and do not care about reproducing the
+idiosyncrasies and limitations of a particular bit of real-world
+hardware.
+
+Supported devices
+-----------------
+
+ * PCI/PCIe devices
+ * 8 virtio-mmio transport devices
+ * 16550A UART
+ * Goldfish RTC
+ * SiFive Test device for poweroff and reboot
+ * SMP (OpenRISC multicore using ompic)
+
+Boot options
+------------
+
+The virt machine can be started using the ``-kernel`` and ``-initrd`` options
+to load a Linux kernel and optional disk image. For example:
+
+.. code-block:: bash
+
+  $ qemu-system-or1k -cpu or1220 -M or1k-sim -nographic \
+        -device virtio-net-device,netdev=user -netdev user,id=user,net=10.9.0.1/24,host=10.9.0.100 \
+        -device virtio-blk-device,drive=d0 -drive file=virt.qcow2,id=d0,if=none,format=qcow2 \
+        -kernel vmlinux \
+        -initrd initramfs.cpio.gz \
+        -m 128
+
+Linux guest kernel configuration
+""""""""""""""""""""""""""""""""
+
+The 'virt_defconfig' for Linux openrisc kernels includes the right drivers for
+the ``virt`` machine.
+
+Hardware configuration information
+""""""""""""""""""""""""""""""""""
+
+The ``virt`` board automatically generates a device tree blob ("dtb") which it
+passes to the guest. This provides information about the addresses, interrupt
+lines and other configuration of the various devices in the system.
+
+The location of the DTB will be passed in register ``r3`` to the guest operating
+system.

docs/system/target-openrisc.rst

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+.. _OpenRISC-System-emulator:
+
+OpenRISC System emulator
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+QEMU can emulate 32-bit OpenRISC CPUs using the ``qemu-system-or1k`` executable.
+
+OpenRISC CPUs are generally built into "system-on-chip" (SoC) designs that run
+on FPGAs.  These SoCs are based on the same core architecture as the or1ksim
+(the original OpenRISC instruction level simulator) which QEMU supports. For
+this reason QEMU does not need to support many different boards to support the
+OpenRISC hardware ecosystem.
+
+The OpenRISC CPU supported by QEMU is the ``or1200``, it supports an MMU and can
+run linux.
+
+Choosing a board model
+======================
+
+For QEMU's OpenRISC system emulation, you must specify which board model you
+want to use with the ``-M`` or ``--machine`` option; the default machine is
+``or1k-sim``.
+
+If you intend to boot Linux, it is possible to have a single kernel image that
+will boot on any of the QEMU machines. To do this one would compile all required
+drivers into the kernel. This is possible because QEMU will create a device tree
+structure that describes the QEMU machine and pass a pointer to the structure to
+the kernel.  The kernel can then use this to configure itself for the machine.
+
+However, typically users will have specific firmware images for a specific machine.
+
+If you already have a system image or a kernel that works on hardware and you
+want to boot with QEMU, check whether QEMU lists that machine in its ``-machine
+help`` output. If it is listed, then you can probably use that board model. If
+it is not listed, then unfortunately your image will almost certainly not boot
+on QEMU. (You might be able to extract the filesystem and use that with a
+different kernel which boots on a system that QEMU does emulate.)
+
+If you don't care about reproducing the idiosyncrasies of a particular
+bit of hardware, such as small amount of RAM, no PCI or other hard disk, etc.,
+and just want to run Linux, the best option is to use the ``virt`` board. This
+is a platform which doesn't correspond to any real hardware and is designed for
+use in virtual machines. You'll need to compile Linux with a suitable
+configuration for running on the ``virt`` board. ``virt`` supports PCI, virtio
+and large amounts of RAM.
+
+Board-specific documentation
+============================
+
+..
+   This table of contents should be kept sorted alphabetically
+   by the title text of each file, which isn't the same ordering
+   as an alphabetical sort by filename.
+
+.. toctree::
+   :maxdepth: 1
+
+   openrisc/or1k-sim
+   openrisc/virt
+
+Emulated CPU architecture support
+=================================
+
+.. toctree::
+   openrisc/emulation
+
+OpenRISC CPU features
+=====================
+
+.. toctree::
+   openrisc/cpu-features

docs/system/targets.rst

@@ -21,6 +21,7 @@ Contents:
    target-m68k
    target-mips
    target-ppc
+   target-openrisc
    target-riscv
    target-rx
    target-s390x