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213 lines
7.2 KiB
213 lines
7.2 KiB
.. _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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Debugging: |
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- kms_plane: some test cases are failing due to timeout on capturing CRC; |
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- kms_flip: when running test cases in sequence, some successful individual |
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test cases are failing randomly; when individually, some successful test |
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cases display in the log the following error:: |
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[drm:vkms_prepare_fb [vkms]] ERROR vmap failed: -4 |
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Virtual hardware (vblank-less) mode: |
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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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- Multiple overlay planes. [Good to get started] |
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- Clearing primary plane: clear primary plane before plane composition (at the |
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start) for correctness of pixel blend ops. It also guarantees alpha channel |
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is cleared in the target buffer for stable crc. [Good to get started] |
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- ARGB format on primary plane: blend the primary plane into background with |
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translucent alpha. |
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- Support when the primary plane isn't exactly matching the output size: blend |
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the primary plane into the black background. |
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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. They are good options for internship |
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project. |
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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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[Good to get started] |
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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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