Public bug reported:
### Description of Problem
Following an update to linux-image-7.0.0-28-generic, external HDMI display
output via internal DisplayPort bridge (card1-DP-1 through card1-DP-4) stopped
functioning completely on an Asus VivoBook. Hot Plug Detect (HPD) fails to
trigger, and no EDID can be read over the DDC/I2C buses.
### Hardware / Environment
- Laptop: ASUS VivoBook
- OS: Ubuntu 26.04 LTS
- GPU/Driver: Intel Graphics (i915)
- Connection: HDMI cable (internal DP-to-HDMI bridge)
### Regression Status
- Working Kernel: 7.0.0-27-generic (EDID reads correctly, dual monitors
functional)
- Broken Kernel: 7.0.0-28-generic (No display output, HPD unresponsive)
### Diagnostics Performed on Broken Kernel (7.0.0-28)
1. `/sys/class/drm/card1-DP-*/status` lists all DP interfaces as `disconnected`
regardless of plug/unplug events.
2. `dmesg -w` yields zero kernel events or warnings when hot-plugging the HDMI
cable.
3. Hardware/Cable isolation: Tested known-good cable and external monitor on a
secondary laptop (working). Hard EC power reset (40-sec hold) performed to
eliminate locked retimer hardware states.
4. `get-edid` scanning:
- Bus 13 (internal eDP panel / Samsung SDC) reads EDID successfully.
- External DDC buses (4-12, 14-17) return `No EDID on bus X`.
- Bus 2 returns `Device or resource busy`.
### Expected Behavior
Plugging in the HDMI cable should trigger an HPD interrupt, populate the EDID
over the corresponding i915 GMBUS/AUX channel, and enable output on
`card1-DP-*`.
### Actual Behavior
HDMI PHY appears unpowered or HPD polling is completely disabled in kernel
7.0.0-28-generic.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-28-generic 7.0.0-28.28
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.0-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Thu Jul 30 08:06:59 2026
InstallationDate: Installed on 2026-06-07 (53 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
MachineType: ASUSTeK COMPUTER INC. ASUS Vivobook Pro 15 N6506MJ_Q543MJ
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-28-generic
root=UUID=b6ccde3d-cec4-438f-ae32-45c982804ea1 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: 10/13/2025
dmi.bios.release: 5.32
dmi.bios.vendor: American Megatrends International, LLC.
dmi.bios.version: N6506MJ.313
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: N6506MJ
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: 1.0
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: 1.0
dmi.ec.firmware.release: 18.239
dmi.modalias:
dmi:bvnAmericanMegatrendsInternational,LLC.:bvrN6506MJ.313:bd10/13/2025:br5.32:efr18.239:svnASUSTeKCOMPUTERINC.:pnASUSVivobookPro15N6506MJ_Q543MJ:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnN6506MJ:rvr1.0:cvnASUSTeKCOMPUTERINC.:ct10:cvr1.0:sku:pfaASUSVivobookPro15:
dmi.product.family: ASUS Vivobook Pro 15
dmi.product.name: ASUS Vivobook Pro 15 N6506MJ_Q543MJ
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK COMPUTER INC.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2162111
Title:
[Regression] HDMI external display via Intel i915/DP bridge
unpowered/undetected (7.0.0-27 -> 7.0.0-28)
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