AMDGPU driver adds HDMI 2.2 FRL support for Linux 7.4

AMDGPU driver fixes for Linux 7.4 include support for HDMI 2.2 Fixed Rate Link signaling, which defines three new per-lane speeds—16, 20, and 24 Gbps—that exceed HDMI 2.1's 12 Gbps ceiling. Prior to these patches, a display advertising HDMI 2.2 FRL rates was misidentified as lacking FRL support entirely, causing the link to train at substantially lower bandwidth than the monitor could handle. The fix extends the kernel's DRM EDID parser to decode the new Max_FRL_Rate values (7, 8, and 9) in the HF-SCDB block and maps them to the rate indices used by AMDGPU's display core. This arrives alongside Linux 7.4's default enablement of HDMI 2.1 FRL, FreeSync/VRR, and ALLM features.

The patches were submitted by AMD engineer Fangzhi Zuo as part of a broader AMDGPU fixes pull request that also addresses UALink, GPU reset, SR-IOV, DCN, and FreeSync/VRR defects. If accepted through the DRM fixes path this week, the changes will reach Linus Torvalds in time for Linux 7.4-rc2.

HDMI 2.2 FRL implementation in AMDGPU

• EDID parsing: Patch 1 extends the kernel's DRM EDID parser to decode three new HDMI 2.2 FRL rates (16, 20, 24 Gbps per lane) represented as Max_FRL_Rate values 7, 8, and 9 in the HF-SCDB (HDMI Forum Source Capability Data Block).
• Rate ceiling fix: The previous AMDGPU code capped FRL recognition at HDMI 2.1's 12 Gbps per lane, causing HDMI 2.2 sinks to be treated as FRL-unsupported and trained at suboptimal link speeds.
• DC core mapping: Patch 2 maps the newly parsed HDMI 2.2 rates to the FRL rate index used by AMDGPU's display core (amdgpu_dm), enabling proper link training negotiation with high-bandwidth displays.
• Test coverage: The fix includes expanded KUnit test coverage for the FRL rate parsing and mapping logic.
• Integration path: The changes are routed through the DRM subsystem fixes pipeline for inclusion in Linux 7.4-rc2, alongside unrelated corrections for UALink, GPU reset, SR-IOV, and DCN subsystems.

Why it matters

For Linux desktop users with RDNA-based GPUs and next-generation high-refresh-rate 4K or 8K displays, proper HDMI 2.2 FRL negotiation eliminates a silent performance regression where monitors would run below their rated bandwidth. This also positions the AMDGPU driver to support forthcoming display hardware that depends on the higher FRL rates, reducing the gap between Linux and proprietary driver display feature parity. Distribution maintainers tracking Linux 7.4 will receive this fix automatically through the stable DRM fixes path without requiring backport effort.