docs/system/devices/igb: Add igb documentation

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

MAINTAINERS

@@ -2252,6 +2252,7 @@ F: tests/qtest/libqos/e1000e.*
 igb
 M: Akihiko Odaki <akihiko.odaki@daynix.com>
 S: Maintained
+F: docs/system/devices/igb.rst
 F: hw/net/igb*
 F: tests/avocado/igb.py
 F: tests/qtest/igb-test.c

docs/system/device-emulation.rst

@@ -93,3 +93,4 @@ Emulated Devices
    devices/virtio-pmem.rst
    devices/vhost-user-rng.rst
    devices/canokey.rst
+   devices/igb.rst

docs/system/devices/igb.rst

@@ -0,0 +1,71 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+.. _igb:
+
+igb
+---
+
+igb is a family of Intel's gigabit ethernet controllers. In QEMU, 82576
+emulation is implemented in particular. Its datasheet is available at [1]_.
+
+This implementation is expected to be useful to test SR-IOV networking without
+requiring physical hardware.
+
+Limitations
+===========
+
+This igb implementation was tested with Linux Test Project [2]_ and Windows HLK
+[3]_ during the initial development. The command used when testing with LTP is:
+
+.. code-block:: shell
+
+  network.sh -6mta
+
+Be aware that this implementation lacks many functionalities available with the
+actual hardware, and you may experience various failures if you try to use it
+with a different operating system other than Linux and Windows or if you try
+functionalities not covered by the tests.
+
+Using igb
+=========
+
+Using igb should be nothing different from using another network device. See
+:ref:`pcsys_005fnetwork` in general.
+
+However, you may also need to perform additional steps to activate SR-IOV
+feature on your guest. For Linux, refer to [4]_.
+
+Developing igb
+==============
+
+igb is the successor of e1000e, and e1000e is the successor of e1000 in turn.
+As these devices are very similar, if you make a change for igb and the same
+change can be applied to e1000e and e1000, please do so.
+
+Please do not forget to run tests before submitting a change. As tests included
+in QEMU is very minimal, run some application which is likely to be affected by
+the change to confirm it works in an integrated system.
+
+Testing igb
+===========
+
+A qtest of the basic functionality is available. Run the below at the build
+directory:
+
+.. code-block:: shell
+
+  meson test qtest-x86_64/qos-test
+
+ethtool can test register accesses, interrupts, etc. It is automated as an
+Avocado test and can be ran with the following command:
+
+.. code:: shell
+
+  make check-avocado AVOCADO_TESTS=tests/avocado/igb.py
+
+References
+==========
+
+.. [1] https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/82576eb-gigabit-ethernet-controller-datasheet.pdf
+.. [2] https://github.com/linux-test-project/ltp
+.. [3] https://learn.microsoft.com/en-us/windows-hardware/test/hlk/
+.. [4] https://docs.kernel.org/PCI/pci-iov-howto.html