New Patches Provide HDMI 1.4 3D Mode Support For AMD Radeon Graphics On Linux

It turns out one of the feature limitations of the AMDGPU Linux graphics driver is HDMI 1.4 3D output support with frame packing, top-and-bottom, and side-by-side options for transmitting simultaneous video streams. I wasn't aware of this limitation for the lack of any 3D displays and many Linux enthusiasts/gamers as well, but if you happen to have a compatible HDMI 1.4 3D display, there are pending patches to finally make this a reality. Independent open-source developer Adrian Betschart posted the set of three patches, amounting to just some ~60 lines of new code for enabling HDMI 1.4 3D mode support with the AMDGPU kernel driver. Betschart noted the DRM EDID parser already derived the 3D output information from the HDMI VSDB but was never taken advantage of by the AMDGPPU driver, even with the Intel i915 driver using it for a decade. Indeed, back in 2012 noting on Phoronix of Intel Linux support for the HDMI 3D modes. Betschart added that this HDMI 1.4 3D output support with the AMDGPU driver works with media players producing 3D frames like MPV and Kodi. He elaborated on the usage: "These three patches add it for native HDMI connectors, in the simplest form that works on the hardware: the source packs both views into the frame and the display core scans that frame out as ordinary 2D; the only 3D-specific output is the HDMI vendor infoframe. The reason it has to be done this way is in patch 1: any of DC's stereo timing formats, including the SW_PACKED ones, makes the hardware treat the surface as two views and paint the whole frame into each half. Patch 2 adds the 3D_Ext_Data byte to the top-and-bottom vendor infoframe, without which at least JVC D-ILA projectors do not engage 3D (Amlogic sources send it, which is why those work with the same projector). Patch 3 sizes the stream and the plane viewport by the doubled frame-packing timing so each eye receives its own view rather than a stretched copy of the first. Tested on a Radeon RX 7600 (Navi 33, DCN 3.2.1) driving a JVC DLA-RS4100 through an HDFury VRROOM, with Kodi (LibreELEC, GBM) as the source, on a 7.2.3 kernel carrying these patches; the series here is rebased onto amd-staging-drm-next and compile-tested there. All three layouts engage the projector's 3D mode at 1920x1080p24, RGB 12 bpc, with correct per-eye geometry (row-coded test frames read back through each eye of shutter glasses) and correct eye assignment; frame packing is also the format the projector uses for Blu-ray 3D." Those interested can learn more about this proposed HDMI 1.4 3D mode support for the AMDGPU driver via this patch series now out for review on the Linux kernel mailing list.