Posted today were new Intel kernel graphics driver patches for Linux to enable Adaptive Sync SDP (Secondary Data Packet) handling for Panel Replay and Auxless Adaptive Link Power Management (ALPM) modes.
Going back to early 2024 was a prior incarnation of patches working on Adaptive Sync SDP support that is important particularly around Adaptive Sync / Variable Refresh Rate support when using DisplayPort adapters / protocol converters.
Intel software engineer Ankit Nautiyal summed up the latest Intel Adaptive Sync work for their open-source Linux driver as:
“Enable Adaptive Sync SDP for Panel replay + auxless ALPM. First few patches are fixes in existing AS SDP enablement. patches add the support to send AS SDP for Panel replay with Link ON and with auxless ALPM (Link-Off).
Apart from few patches from [other patch series] new changes include:
– Some clean up in drm/dp Macros
– Add new DPCD bit to get FAVT PAYLOAD FIELDS PARSING SUPPORT.
– Add AS SDP version and PR and VRR specific bits in drm_dp.h.
– Modify AS SDP compute config to accomodate PR with Link On and Link Off.
– Program Downspread Ctrl DPCD bits.
– Make way for T1 and T2 AS SDP transmission timing/position.”
The patch series is now out for review for improving the Adaptive Sync SDP support with the Intel driver.
“Currently we do not support VRR with HDMI so skip vrr compute config step for all DP branch devices.
…
Among non-MST DP branch devices, only an HDMI 2.1 sink connected via a PCON could support VRR. However, supporting VRR through a PCON requires non-trivial changes that are not implemented yet. Until that support exists, avoid VRR on all DP branch devices.”
One of the patches also does confirm that the Intel Linux driver is still not supporting Variable Refresh Rate with HDMI (2.1), presumably in part due to the ongoing mess with the HDMI Forum.
