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<h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/gpu/vkms.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> </div> </div> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main">   <section id="drm-vkms-virtual-kernel-modesetting"> <span id="vkms"></span><h1>drm/vkms Virtual Kernel Modesetting<a class="headerlink" href="#drm-vkms-virtual-kernel-modesetting" title="Permalink to this heading">露</a></h1> <p>VKMS is a software-only model of a KMS driver that is useful for testing and for running X (or similar) on headless machines. VKMS aims to enable a virtual display with no need of a hardware display capability, releasing the GPU in DRM API tests.</p> <section id="setup"> <h2>Setup<a class="headerlink" href="#setup" title="Permalink to this heading">露</a></h2> <p>The VKMS driver can be setup with the following steps:</p> <p>To check if VKMS is loaded, run:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>lsmod | grep vkms </pre></div> </div> <p>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:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>make nconfig Go to `Device Drivers> Graphics support` Enable `Virtual KMS (EXPERIMENTAL)` </pre></div> </div> <p>Compile and build the kernel for the changes to get reflected. Now, to load the driver, use:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>sudo modprobe vkms </pre></div> </div> <p>On running the lsmod command now, the VKMS driver will appear listed. You can also observe the driver being loaded in the dmesg logs.</p> <p>The VKMS driver has optional features to simulate different kinds of hardware, which are exposed as module options. You can use the <cite>modinfo</cite> command to see the module options for vkms:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>modinfo vkms </pre></div> </div> <p>Module options are helpful when testing, and enabling modules can be done while loading vkms. For example, to load vkms with cursor enabled, use:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>sudo modprobe vkms enable_cursor=1 </pre></div> </div> <p>To disable the driver, use</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>sudo modprobe -r vkms </pre></div> </div> </section> <section id="testing-with-igt"> <h2>Testing With IGT<a class="headerlink" href="#testing-with-igt" title="Permalink to this heading">露</a></h2> <p>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 <a class="reference external" href="https://gitlab.freedesktop.org/drm/igt-gpu-tools">here</a> .</p> <p>The tests need to be run without a compositor, so you need to switch to text only mode. You can do this by:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>sudo systemctl isolate multi-user.target </pre></div> </div> <p>To return to graphical mode, do:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>sudo systemctl isolate graphical.target </pre></div> </div> <p>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:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>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> </pre></div> </div> <p>For example, to test the functionality of the writeback library, we can run the kms_writeback test:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>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 </pre></div> </div> <p>You can also run subtests if you do not want to run the entire test:</p> <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>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 </pre></div> </div> </section> <section id="todo"> <h2>TODO<a class="headerlink" href="#todo" title="Permalink to this heading">露</a></h2> <p>If you want to do any of the items listed below, please share your interest with VKMS maintainers.</p> <section id="igt-better-support"> <h3>IGT better support<a class="headerlink" href="#igt-better-support" title="Permalink to this heading">露</a></h3> <p>Debugging:</p> <ul class="simple"> <li><p>kms_plane: some test cases are failing due to timeout on capturing CRC;</p></li> </ul> <p>Virtual hardware (vblank-less) mode:</p> <ul class="simple"> <li><p>VKMS already has support for vblanks simulated via hrtimers, which can be tested with kms_flip test; in some way, we can say that VKMS already mimics the real hardware vblank. However, we also have virtual hardware that does not support vblank interrupt and completes page_flip events right away; in this case, compositor developers may end up creating a busy loop on virtual hardware. It would be useful to support Virtual Hardware behavior in VKMS because this can help compositor developers to test their features in multiple scenarios.</p></li> </ul> </section> <section id="add-plane-features"> <h3>Add Plane Features<a class="headerlink" href="#add-plane-features" title="Permalink to this heading">露</a></h3> <p>There鈥檚 lots of plane features we could add support for:</p> <ul class="simple"> <li><p>Add background color KMS property[Good to get started].</p></li> <li><p>Scaling.</p></li> <li><p>Additional buffer formats, especially YUV formats for video like NV12. Low/high bpp RGB formats would also be interesting.</p></li> <li><p>Async updates (currently only possible on cursor plane using the legacy cursor api).</p></li> </ul> <p>For all of these, we also want to review the igt test coverage and make sure all relevant igt testcases work on vkms. They are good options for internship project.</p> </section> <section id="runtime-configuration"> <h3>Runtime Configuration<a class="headerlink" href="#runtime-configuration" title="Permalink to this heading">露</a></h3> <p>We want to be able to reconfigure vkms instance without having to reload the module. Use/Test-cases:</p> <ul class="simple"> <li><p>Hotplug/hotremove connectors on the fly (to be able to test DP MST handling of compositors).</p></li> <li><p>Configure planes/crtcs/connectors (we鈥檇 need some code to have more than 1 of them first).</p></li> <li><p>Change output configuration: Plug/unplug screens, change EDID, allow changing the refresh rate.</p></li> </ul> <p>The currently proposed solution is to expose vkms configuration through configfs. All existing module options should be supported through configfs too.</p> </section> <section id="writeback-support"> <h3>Writeback support<a class="headerlink" href="#writeback-support" title="Permalink to this heading">露</a></h3> <ul class="simple"> <li><p>The writeback and CRC capture operations share the use of composer_enabled boolean to ensure vblanks. Probably, when these operations work together, composer_enabled needs to refcounting the composer state to proper work. [Good to get started]</p></li> <li><p>Add support for cloned writeback outputs and related test cases using a cloned output in the IGT kms_writeback.</p></li> <li><p>As a v4l device. This is useful for debugging compositors on special vkms configurations, so that developers see what鈥檚 really going on.</p></li> </ul> </section> <section id="output-features"> <h3>Output Features<a class="headerlink" href="#output-features" title="Permalink to this heading">露</a></h3> <ul class="simple"> <li><p>Variable refresh rate/freesync support. This probably needs prime buffer sharing support, so that we can use vgem fences to simulate rendering in testing. Also needs support to specify the EDID.</p></li> <li><p>Add support for link status, so that compositors can validate their runtime fallbacks when e.g. a Display Port link goes bad.</p></li> </ul> </section> <section id="crc-api-improvements"> <h3>CRC API Improvements<a class="headerlink" href="#crc-api-improvements" title="Permalink to this heading">露</a></h3> <ul class="simple"> <li><p>Optimize CRC computation <code class="docutils literal notranslate"><span class="pre">compute_crc()</span></code> and plane blending <code class="docutils literal notranslate"><span class="pre">blend()</span></code></p></li> </ul> </section> <section id="atomic-check-using-ebpf"> <h3>Atomic Check using eBPF<a class="headerlink" href="#atomic-check-using-ebpf" title="Permalink to this heading">露</a></h3> <p>Atomic drivers have lots of restrictions which are not exposed to userspace in any explicit form through e.g. possible property values. Userspace can only inquiry about these limits through the atomic IOCTL, possibly using the TEST_ONLY flag. Trying to add configurable code for all these limits, to allow compositors to be tested against them, would be rather futile exercise. Instead we could add support for eBPF to validate any kind of atomic state, and implement a library of different restrictions.</p> <p>This needs a bunch of features (plane compositing, multiple outputs, ...) enabled already to make sense.</p> </section> </section> </section> </div> </div> </div> <div class="clearer"></div> </div> <div class="footer"> ©The kernel development community. | Powered by <a href="https://www.sphinx-doc.org/">Sphinx 5.3.0</a> & <a href="https://alabaster.readthedocs.io">Alabaster 0.7.16</a> | <a href="../_sources/gpu/vkms.rst.txt" rel="nofollow">Page source</a> </div> </body> </html>