drm/amd/display - Display Core (DC)

AMD display engine is partially shared with other operating systems; for thisreason, our Display Core Driver is divided into two pieces:

  1. Display Core (DC) contains the OS-agnostic components. Things likehardware programming and resource management are handled here.

  2. Display Manager (DM) contains the OS-dependent components. Hooks to theamdgpu base driver and DRM are implemented here. For example, you can checkdisplay/amdgpu_dm/ folder.

DC Code validation

Maintaining the same code base across multiple OSes requires a lot ofsynchronization effort between repositories and exhaustive validation. In theDC case, we maintain a tree to centralize code from different parts. The sharedrepository has integration tests with our Internal Linux CI farm, and we run acomprehensive set of IGT tests in various AMD GPUs/APUs (mostly recent dGPUsand APUs). Our CI also checks ARM64/32, PPC64/32, and x86_64/32 compilationwith DCN enabled and disabled.

When we upstream a new feature or some patches, we pack them in a patchset withthe prefixDC Patches for <DATE>, which is created based on the latestamd-staging-drm-next. All ofthose patches are under a DC version tested as follows:

  • Ensure that every patch compiles and the entire series pass our set of IGTtest in different hardware.

  • Prepare a branch with those patches for our validation team. If there is anerror, a developer will debug as fast as possible; usually, a simple bisectin the series is enough to point to a bad change, and two possible actionsemerge: fix the issue or drop the patch. If it is not an easy fix, the badpatch is dropped.

  • Finally, developers wait a few days for community feedback before we mergethe series.

It is good to stress that the test phase is something that we take extremelyseriously, and we never merge anything that fails our validation. Follows anoverview of our test set:

  1. Manual test

    • Multiple Hotplugs with DP and HDMI.

    • Stress test with multiple display configuration changes via the user interface.

    • Validate VRR behaviour.

    • Check PSR.

    • Validate MPO when playing video.

    • Test more than two displays connected at the same time.

    • Check suspend/resume.

    • Validate FPO.

    • Check MST.

  2. Automated test

    • IGT tests in a farm with GPUs and APUs that support DCN and DCE.

    • Compilation validation with the latest GCC and Clang from LTS distro.

    • Cross-compilation for PowerPC 64/32, ARM 64/32, and x86 32.

In terms of test setup for CI and manual tests, we usually use:

  1. The latest Ubuntu LTS.

  2. In terms of userspace, we only use fully updated open-source componentsprovided by the distribution official package manager.

  3. Regarding IGT, we use the latest code from the upstream.

  4. Most of the manual tests are conducted in the GNome but we also use KDE.

Notice that someone from our test team will always reply to the cover letterwith the test report.

DC Information

The display pipe is responsible for “scanning out” a rendered frame from theGPU memory (also called VRAM, FrameBuffer, etc.) to a display. In other words,it would:

  1. Read frame information from memory;

  2. Perform required transformation;

  3. Send pixel data to sink devices.

If you want to learn more about our driver details, take a look at the belowtable of content: