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Update vkms documentation to contain usage of `modinfo` command and steps to load vkms with module options enabled. Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com> Reviewed-by: Melissa Wen <melissa.srw@gmail.com> Signed-off-by: Melissa Wen <melissa.srw@gmail.com> Link: https://patchwork.freedesktop.org/patch/msgid/4fbc6459377c1dcbe8e6648718453d5693f6451c.1610391685.git.sylphrenadin@gmail.com
199 lines
6.7 KiB
ReStructuredText
199 lines
6.7 KiB
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.. _vkms:
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==========================================
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drm/vkms Virtual Kernel Modesetting
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==========================================
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.. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c
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:doc: vkms (Virtual Kernel Modesetting)
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Setup
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=====
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The VKMS driver can be setup with the following steps:
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To check if VKMS is loaded, run::
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lsmod | grep vkms
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This should list the VKMS driver. If no output is obtained, then
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you need to enable and/or load the VKMS driver.
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Ensure that the VKMS driver has been set as a loadable module in your
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kernel config file. Do::
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make nconfig
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Go to `Device Drivers> Graphics support`
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Enable `Virtual KMS (EXPERIMENTAL)`
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Compile and build the kernel for the changes to get reflected.
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Now, to load the driver, use::
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sudo modprobe vkms
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On running the lsmod command now, the VKMS driver will appear listed.
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You can also observe the driver being loaded in the dmesg logs.
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The VKMS driver has optional features to simulate different kinds of hardware,
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which are exposed as module options. You can use the `modinfo` command
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to see the module options for vkms::
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modinfo vkms
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Module options are helpful when testing, and enabling modules
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can be done while loading vkms. For example, to load vkms with cursor enabled,
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use::
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sudo modprobe vkms enable_cursor=1
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To disable the driver, use ::
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sudo modprobe -r vkms
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Testing With IGT
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================
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The IGT GPU Tools is a test suite used specifically for debugging and
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development of the DRM drivers.
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The IGT Tools can be installed from
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`here <https://gitlab.freedesktop.org/drm/igt-gpu-tools>`_ .
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The tests need to be run without a compositor, so you need to switch to text
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only mode. You can do this by::
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sudo systemctl isolate multi-user.target
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To return to graphical mode, do::
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sudo systemctl isolate graphical.target
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Once you are in text only mode, you can run tests using the --device switch
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or IGT_DEVICE variable to specify the device filter for the driver we want
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to test. IGT_DEVICE can also be used with the run-test.sh script to run the
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tests for a specific driver::
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sudo ./build/tests/<name of test> --device "sys:/sys/devices/platform/vkms"
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sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/<name of test>
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sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t <name of test>
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For example, to test the functionality of the writeback library,
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we can run the kms_writeback test::
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sudo ./build/tests/kms_writeback --device "sys:/sys/devices/platform/vkms"
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sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_writeback
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sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t kms_writeback
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You can also run subtests if you do not want to run the entire test::
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sudo ./build/tests/kms_flip --run-subtest basic-plain-flip --device "sys:/sys/devices/platform/vkms"
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sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip
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TODO
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====
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If you want to do any of the items listed below, please share your interest
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with VKMS maintainers.
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IGT better support
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------------------
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- Investigate: (1) test cases on kms_plane that are failing due to timeout on
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capturing CRC; (2) when running kms_flip test cases in sequence, some
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successful individual test cases are failing randomly.
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- VKMS already has support for vblanks simulated via hrtimers, which can be
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tested with kms_flip test; in some way, we can say that VKMS already mimics
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the real hardware vblank. However, we also have virtual hardware that does
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not support vblank interrupt and completes page_flip events right away; in
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this case, compositor developers may end up creating a busy loop on virtual
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hardware. It would be useful to support Virtual Hardware behavior in VKMS
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because this can help compositor developers to test their features in
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multiple scenarios.
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Add Plane Features
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------------------
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There's lots of plane features we could add support for:
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- Real overlay planes, not just cursor.
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- Full alpha blending on all planes.
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- Rotation, scaling.
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- Additional buffer formats, especially YUV formats for video like NV12.
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Low/high bpp RGB formats would also be interesting.
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- Async updates (currently only possible on cursor plane using the legacy
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cursor api).
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For all of these, we also want to review the igt test coverage and make sure
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all relevant igt testcases work on vkms.
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Prime Buffer Sharing
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--------------------
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- Syzbot report - WARNING in vkms_gem_free_object:
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https://syzkaller.appspot.com/bug?extid=e7ad70d406e74d8fc9d0
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Runtime Configuration
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---------------------
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We want to be able to reconfigure vkms instance without having to reload the
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module. Use/Test-cases:
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- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling
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of compositors).
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- Configure planes/crtcs/connectors (we'd need some code to have more than 1 of
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them first).
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- Change output configuration: Plug/unplug screens, change EDID, allow changing
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the refresh rate.
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The currently proposed solution is to expose vkms configuration through
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configfs. All existing module options should be supported through configfs
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too.
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Writeback support
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-----------------
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- The writeback and CRC capture operations share the use of composer_enabled
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boolean to ensure vblanks. Probably, when these operations work together,
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composer_enabled needs to refcounting the composer state to proper work.
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- Add support for cloned writeback outputs and related test cases using a
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cloned output in the IGT kms_writeback.
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- As a v4l device. This is useful for debugging compositors on special vkms
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configurations, so that developers see what's really going on.
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Output Features
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---------------
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- Variable refresh rate/freesync support. This probably needs prime buffer
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sharing support, so that we can use vgem fences to simulate rendering in
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testing. Also needs support to specify the EDID.
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- Add support for link status, so that compositors can validate their runtime
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fallbacks when e.g. a Display Port link goes bad.
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CRC API Improvements
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--------------------
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- Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``
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Atomic Check using eBPF
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-----------------------
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Atomic drivers have lots of restrictions which are not exposed to userspace in
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any explicit form through e.g. possible property values. Userspace can only
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inquiry about these limits through the atomic IOCTL, possibly using the
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TEST_ONLY flag. Trying to add configurable code for all these limits, to allow
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compositors to be tested against them, would be rather futile exercise. Instead
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we could add support for eBPF to validate any kind of atomic state, and
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implement a library of different restrictions.
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This needs a bunch of features (plane compositing, multiple outputs, ...)
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enabled already to make sense.
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