modeset: honor forced FRL rate during link assessment

[Rohithmatham12]

Summary

• Treat nvidia-modeset.force_frl_rate as an explicit opt-in to use EDID-declared FRL capabilities during HDMI FRL link assessment.
• Leave the default physical link-training assessment path unchanged when force_frl_rate=0.
• Update the module parameter description so modinfo reflects the EDID-capability behavior.

This helps forced/headless HDMI connectors where a valid override EDID advertises FRL (for example Max_FRL_Rate=6) but physical link assessment cannot complete because there is no real sink handshake, causing high-bandwidth modes such as 4K120 to be pruned.

Fixes #1184.

Testing

• git diff --check
• make -C kernel-open -n modules
  • Reached the kernel build handoff and then stopped in this macOS workspace because /lib/modules/25.5.0/build is not present.
• Reporter validation on Force-enabled virtual connector won't bring up FRL — capped at 4K60 despite EDID Max_FRL_Rate=6 (blocks headless 4K120 Sunshine/Moonlight) #1184 / this PR:
  • Hardware/software: RTX 3060 Ti, nvidia-open 610.43.02, kernel 7.0.11
  • Boot setup: drm.edid_firmware=HDMI-A-1:edid/<file> video=HDMI-A-1:e
  • Override EDID advertises Max_FRL_Rate=6 plus VIC 118
  • Stock driver with nvidia-modeset.force_frl_rate=1 and =2 still stayed capped at 4K60
  • With this patch plus nvidia-modeset.force_frl_rate=1, 3840x2160@119.88 appears and sets on the force-enabled HDMI connector
  • HDR also enables and Sunshine HEVC Main10 streaming was confirmed end to end
  • Custom high-bandwidth DisplayID timings such as 3024x1890@120 and 2752x2064@120 also validate and set

[Rohithmatham12]

Thanks for testing and confirming the HDMI force-enabled connector case. I updated the PR description with your validation details and marked the PR ready for review.

The key confirmation is that stock nvidia-modeset.force_frl_rate=1/2 still capped the forced HDMI connector at 4K60, while this patch plus nvidia-modeset.force_frl_rate=1 exposed and set 3840x2160@119.88, with HDR/Sunshine HEVC Main10 working end to end.

[HarryAnkers]

Hardware validation on RTX 3060 Ti (GA104), nvidia-open 610.43.02, kernel 7.0.11, KDE Plasma 6.6 Wayland, headless HDMI connector force-enabled via drm.edid_firmware=HDMI-A-1:edid/<file> video=HDMI-A-1:e with an EDID declaring Max_FRL_Rate=6 and VIC 118 (3840x2160@120):

Without this patch (stock 610.43.02): force_frl_rate=1 and =2 both load but the connector stays pruned to 4K60, with no FRL messages in dmesg at all — the FRL path is never entered.

With this patch + nvidia-modeset.force_frl_rate=1:

• Patched module confirmed loaded (updated force_frl_rate parm description visible in modinfo).
• 3840x2160@119.88 appears in the mode list and sets successfully. The driver logs nvidia-modeset: WARNING: GPU:0: HDMI FRL link training failed. and proceeds with the modeset — sensible for a sink-less connector.
• HDR enables on top of the 4K120 mode; verified end to end with Sunshine KMS capture encoding HEVC Main10.
• Also exercised with higher custom timings (3024x1890@120 and 2752x2064@120 at ~764 MHz pixel clock, injected via a DisplayID extension block) — both validate and set under the forced FRL.
• Regression check: behavior with force_frl_rate=0 (default) unchanged, and a physically connected monitor on the same GPU behaves normally.

This is exactly the headless HDMI 2.1 setup from #1184 — works as designed. Happy to run any additional tests.