drm/vkms: Add setup and testing information

Update the vkms documentation to contain steps to:

 - setup the vkms driver
 - run tests using igt
Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201209190453.c6kp5winikr55n3i@adolin

Documentation/gpu/vkms.rst

@@ -7,6 +7,76 @@
 .. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c
    :doc: vkms (Virtual Kernel Modesetting)
 
+Setup
+=====
+
+The VKMS driver can be setup with the following steps:
+
+To check if VKMS is loaded, run::
+
+  lsmod | grep vkms
+
+This should list the VKMS driver. If no output is obtained, then
+you need to enable and/or load the VKMS driver.
+Ensure that the VKMS driver has been set as a loadable module in your
+kernel config file. Do::
+
+  make nconfig
+
+  Go to `Device Drivers> Graphics support`
+
+  Enable `Virtual KMS (EXPERIMENTAL)`
+
+Compile and build the kernel for the changes to get reflected.
+Now, to load the driver, use::
+
+  sudo modprobe vkms
+
+On running the lsmod command now, the VKMS driver will appear listed.
+You can also observe the driver being loaded in the dmesg logs.
+
+To disable the driver, use ::
+
+  sudo modprobe -r vkms
+
+Testing With IGT
+================
+
+The IGT GPU Tools is a test suite used specifically for debugging and
+development of the DRM drivers.
+The IGT Tools can be installed from
+`here <https://gitlab.freedesktop.org/drm/igt-gpu-tools>`_ .
+
+The tests need to be run without a compositor, so you need to switch to text
+only mode. You can do this by::
+
+  sudo systemctl isolate multi-user.target
+
+To return to graphical mode, do::
+
+  sudo systemctl isolate graphical.target
+
+Once you are in text only mode, you can run tests using the --device switch
+or IGT_DEVICE variable to specify the device filter for the driver we want
+to test. IGT_DEVICE can also be used with the run-test.sh script to run the
+tests for a specific driver::
+
+  sudo ./build/tests/<name of test> --device "sys:/sys/devices/platform/vkms"
+  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/<name of test>
+  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t <name of test>
+
+For example, to test the functionality of the writeback library,
+we can run the kms_writeback test::
+
+  sudo ./build/tests/kms_writeback --device "sys:/sys/devices/platform/vkms"
+  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_writeback
+  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t kms_writeback
+
+You can also run subtests if you do not want to run the entire test::
+
+  sudo ./build/tests/kms_flip --run-subtest basic-plain-flip --device "sys:/sys/devices/platform/vkms"
+  sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip
+
 TODO
 ====