1.. _vkms: 2 3========================================== 4 drm/vkms Virtual Kernel Modesetting 5========================================== 6 7.. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c 8 :doc: vkms (Virtual Kernel Modesetting) 9 10Setup 11===== 12 13The VKMS driver can be setup with the following steps: 14 15To check if VKMS is loaded, run:: 16 17 lsmod | grep vkms 18 19This should list the VKMS driver. If no output is obtained, then 20you need to enable and/or load the VKMS driver. 21Ensure that the VKMS driver has been set as a loadable module in your 22kernel config file. Do:: 23 24 make nconfig 25 26 Go to `Device Drivers> Graphics support` 27 28 Enable `Virtual KMS (EXPERIMENTAL)` 29 30Compile and build the kernel for the changes to get reflected. 31Now, to load the driver, use:: 32 33 sudo modprobe vkms 34 35On running the lsmod command now, the VKMS driver will appear listed. 36You can also observe the driver being loaded in the dmesg logs. 37 38The VKMS driver has optional features to simulate different kinds of hardware, 39which are exposed as module options. You can use the `modinfo` command 40to see the module options for vkms:: 41 42 modinfo vkms 43 44Module options are helpful when testing, and enabling modules 45can be done while loading vkms. For example, to load vkms with cursor enabled, 46use:: 47 48 sudo modprobe vkms enable_cursor=1 49 50To disable the driver, use :: 51 52 sudo modprobe -r vkms 53 54Testing With IGT 55================ 56 57The IGT GPU Tools is a test suite used specifically for debugging and 58development of the DRM drivers. 59The IGT Tools can be installed from 60`here <https://gitlab.freedesktop.org/drm/igt-gpu-tools>`_ . 61 62The tests need to be run without a compositor, so you need to switch to text 63only mode. You can do this by:: 64 65 sudo systemctl isolate multi-user.target 66 67To return to graphical mode, do:: 68 69 sudo systemctl isolate graphical.target 70 71Once you are in text only mode, you can run tests using the --device switch 72or IGT_DEVICE variable to specify the device filter for the driver we want 73to test. IGT_DEVICE can also be used with the run-test.sh script to run the 74tests for a specific driver:: 75 76 sudo ./build/tests/<name of test> --device "sys:/sys/devices/platform/vkms" 77 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/<name of test> 78 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t <name of test> 79 80For example, to test the functionality of the writeback library, 81we can run the kms_writeback test:: 82 83 sudo ./build/tests/kms_writeback --device "sys:/sys/devices/platform/vkms" 84 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_writeback 85 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t kms_writeback 86 87You can also run subtests if you do not want to run the entire test:: 88 89 sudo ./build/tests/kms_flip --run-subtest basic-plain-flip --device "sys:/sys/devices/platform/vkms" 90 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip 91 92TODO 93==== 94 95If you want to do any of the items listed below, please share your interest 96with VKMS maintainers. 97 98IGT better support 99------------------ 100 101- Investigate: (1) test cases on kms_plane that are failing due to timeout on 102 capturing CRC; (2) when running kms_flip test cases in sequence, some 103 successful individual test cases are failing randomly. 104 105- VKMS already has support for vblanks simulated via hrtimers, which can be 106 tested with kms_flip test; in some way, we can say that VKMS already mimics 107 the real hardware vblank. However, we also have virtual hardware that does 108 not support vblank interrupt and completes page_flip events right away; in 109 this case, compositor developers may end up creating a busy loop on virtual 110 hardware. It would be useful to support Virtual Hardware behavior in VKMS 111 because this can help compositor developers to test their features in 112 multiple scenarios. 113 114Add Plane Features 115------------------ 116 117There's lots of plane features we could add support for: 118 119- Real overlay planes, not just cursor. 120 121- Full alpha blending on all planes. 122 123- Rotation, scaling. 124 125- Additional buffer formats, especially YUV formats for video like NV12. 126 Low/high bpp RGB formats would also be interesting. 127 128- Async updates (currently only possible on cursor plane using the legacy 129 cursor api). 130 131For all of these, we also want to review the igt test coverage and make sure 132all relevant igt testcases work on vkms. 133 134Prime Buffer Sharing 135-------------------- 136 137- Syzbot report - WARNING in vkms_gem_free_object: 138 https://syzkaller.appspot.com/bug?extid=e7ad70d406e74d8fc9d0 139 140Runtime Configuration 141--------------------- 142 143We want to be able to reconfigure vkms instance without having to reload the 144module. Use/Test-cases: 145 146- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling 147 of compositors). 148 149- Configure planes/crtcs/connectors (we'd need some code to have more than 1 of 150 them first). 151 152- Change output configuration: Plug/unplug screens, change EDID, allow changing 153 the refresh rate. 154 155The currently proposed solution is to expose vkms configuration through 156configfs. All existing module options should be supported through configfs 157too. 158 159Writeback support 160----------------- 161 162- The writeback and CRC capture operations share the use of composer_enabled 163 boolean to ensure vblanks. Probably, when these operations work together, 164 composer_enabled needs to refcounting the composer state to proper work. 165 166- Add support for cloned writeback outputs and related test cases using a 167 cloned output in the IGT kms_writeback. 168 169- As a v4l device. This is useful for debugging compositors on special vkms 170 configurations, so that developers see what's really going on. 171 172Output Features 173--------------- 174 175- Variable refresh rate/freesync support. This probably needs prime buffer 176 sharing support, so that we can use vgem fences to simulate rendering in 177 testing. Also needs support to specify the EDID. 178 179- Add support for link status, so that compositors can validate their runtime 180 fallbacks when e.g. a Display Port link goes bad. 181 182CRC API Improvements 183-------------------- 184 185- Optimize CRC computation ``compute_crc()`` and plane blending ``blend()`` 186 187Atomic Check using eBPF 188----------------------- 189 190Atomic drivers have lots of restrictions which are not exposed to userspace in 191any explicit form through e.g. possible property values. Userspace can only 192inquiry about these limits through the atomic IOCTL, possibly using the 193TEST_ONLY flag. Trying to add configurable code for all these limits, to allow 194compositors to be tested against them, would be rather futile exercise. Instead 195we could add support for eBPF to validate any kind of atomic state, and 196implement a library of different restrictions. 197 198This needs a bunch of features (plane compositing, multiple outputs, ...) 199enabled already to make sense. 200