[Bug 2163568] Re: [i915][xe] Failed to read TMDS config: -6 on HDMI-A-1 (Alder Lake-P iGPU, Acer Aspire A715-76G) - external monitor never lights up

** Tags added: kernel-daily-bug -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2163568 Title: [i915][xe] Failed to read TMDS config: -6 on HDMI-A-1 (Alder Lake-P iGPU, Acer Aspire A715-76G) - external monitor never lights up Status in linux package in Ubuntu: New Bug description: Summary ------- External HDMI monitor connected to the Intel iGPU HDMI port never gets a picture. Kernel log repeats every ~16 seconds since boot: [drm] *ERROR* [CONNECTOR:516:HDMI-A-1] Failed to read TMDS config: -6 `xrandr` shows HDMI-1 as "connected" but with an implausible fallback resolution (6880x2880), consistent with a failed EDID/DDC read rather than a real mode. Hardware -------- - Laptop: Acer Aspire A715-76G - iGPU: Intel Alder Lake-P UHD Graphics [8086:46a3] (0000:00:02.0) - HDMI port is wired to this GPU - dGPU: NVIDIA RTX 2050 (GA107), mux-less Optimus, no physical video output of its own - BIOS: InsydeH20, version V1.57 (2026-05-28) - latest available, no relevant multi-monitor/IGD options exposed - OS: Ubuntu 26.04 - Kernel: 7.0.0-29-generic (also reproduced on mainline-adjacent `xe` force-probe of the same kernel) Steps to reproduce ------------------ 1. Cold boot into Ubuntu with an external monitor connected via HDMI. 2. Monitor is detected but shows no signal / no picture. 3. `journalctl -k -b | grep -i -E "tmds|hdmi"` shows repeated "Failed to read TMDS config: -6" (errno -6 = ENXIO) on CONNECTOR:516:HDMI-A-1. What I already ruled out ------------------------- - Cable: tested with a second HDMI cable, same result. - Port/monitor: monitor+cable tested and recognized fine; same monitor works perfectly under Windows 11 on the exact same hardware/cable/port (both cold boot and warm reboot from a fully logged-in Windows session into Ubuntu). - prime-select mode: tested both `nvidia` and `on-demand`, no difference (expected, since the HDMI port is physically on the iGPU, not the dGPU). - Driver: forced the newer `xe` driver via `i915.force_probe=!46a3 xe.force_probe=46a3` - identical "Failed to read TMDS config: -6" error occurs with `xe` as well, just with the `xe` module name in the log instead of `i915`. This points to a failure in the shared GMBUS/DDC/i2c transaction layer, not in driver-specific logic. - BIOS: no Internal Graphics / IGD Multi-Monitor / DVMT / CSM options exist in this InsydeH20 BIOS to test. - Newer kernel: attempted to test mainline v7.1.5, but it fails to boot due to Secure Boot ("bad shim lock signature") since mainline builds are unsigned; not tested with Secure Boot disabled. Expected behavior ----------------- External HDMI monitor should light up on Linux the same way it does on Windows with identical hardware. Additional info ---------------- Please find attached: `journalctl -k -b` output, `lspci -nnk` VGA section, `xrandr` output, and dmesg from apport. ProblemType: Bug DistroRelease: Ubuntu 26.04 Package: linux-image-7.0.0-29-generic 7.0.0-29.29 ProcVersionSignature: Ubuntu 7.0.0-29.29-generic 7.0.12 Uname: Linux 7.0.0-29-generic x86_64 ApportVersion: 2.34.1-0ubuntu0.1 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC0: alex 3919 F.... pipewire alex 3933 F.... wireplumber /dev/snd/seq: alex 3919 F.... pipewire CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Sat Aug 15 14:45:00 2026 InstallationDate: Installed on 2026-08-14 (1 days ago) InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1) MachineType: Acer Aspire A715-76G ProcEnviron: LANG=en_US.UTF-8 PATH=(custom, no user) SHELL=/bin/bash TERM=xterm-256color ProcFB: 0 i915drmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-29-generic root=UUID=34813e31-7b29-4b9f-8baa-6216c89d517a ro quiet splash crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 05/28/2026 dmi.bios.release: 1.57 dmi.bios.vendor: INSYDE Corp. dmi.bios.version: V1.57 dmi.board.asset.tag: Type2 - Board Asset Tag dmi.board.name: Metis_ADP dmi.board.vendor: ADL dmi.board.version: V1.57 dmi.chassis.type: 10 dmi.chassis.vendor: Chassis Manufacturer dmi.chassis.version: Chassis Version dmi.ec.firmware.release: 1.4 dmi.modalias: dmi:bvnINSYDECorp.:bvrV1.57:bd05/28/2026:br1.57:efr1.4:svnAcer:pnAspireA715-76G:pvrV1.57:rvnADL:rnMetis_ADP:rvrV1.57:cvnChassisManufacturer:ct10:cvrChassisVersion:sku0000000000000000:pfaAspire7: dmi.product.family: Aspire 7 dmi.product.name: Aspire A715-76G dmi.product.sku: 0000000000000000 dmi.product.version: V1.57 dmi.sys.vendor: Acer To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2163568/+subscriptions