drm/amd/display - Display Core (DC)

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

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

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

DC Code validation

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

When we upstream a new feature or some patches, we pack them in a patchset with the prefix DC Patches for <DATE>, which is created based on the latest amd-staging-drm-next. All of those patches are under a DC version tested as follows:

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

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

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

It is good to stress that the test phase is something that we take extremely seriously, and we never merge anything that fails our validation. Follows an overview 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 components provided 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 letter with the test report.

DC Information

The display pipe is responsible for “scanning out” a rendered frame from the GPU 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 below table of content: