XPost: linux.debian.kernel   
   From: mk939@ymail.com   
      
   Package: src:linux   
   Version: 6.18.5-1~bpo13+1   
   Severity: important   
   X-Debbugs-Cc: mk939@ymail.com   
      
      
   Greetings.   
      
   When the Kernel command-line parameter 'amdgpu.dc=0' is used, the screen   
   resolution   
   (and TTY font) does not change on boot (i.e. stays whatever was used in GRUB).   
   The boot messages stop updating and a few seconds after, the screen turns off.   
      
   Excerpt from 'journalctl --boot=PREVIOUS_BOOT_HASH':   
   ---   
   Feb 21 08:54:18 x7 systemd[1]: lightdm.service: Main process exited,   
   code=exited, status=1/FAILURE   
   Feb 21 08:54:18 x7 systemd[1]: lightdm.service: Failed with result 'exit-code'.   
   Feb 21 08:54:18 x7 systemd[1]: lightdm.service: Triggering OnFailure=   
   dependencies.   
   ---   
      
   Exerpt from '/var/log/Xorg.0.log.old'   
   ---   
   [    13.170] (II) AMDGPU(0): glamor X acceleration enabled on AMD Radeon RX   
   570 Series (radeonsi, polaris10, ACO, DRM 3.64, 6.18.5+deb13-amd64)   
   [    13.170] (II) AMDGPU(0): glamor detected, initialising EGL layer.   
   [    13.170] (==) AMDGPU(0): TearFree property default: auto   
   [    13.170] (==) AMDGPU(0): VariableRefresh: disabled   
   [    13.170] (==) AMDGPU(0): AsyncFlipSecondaries: disabled   
   [    13.170] (II) AMDGPU(0): KMS Pageflipping: enabled   
   [    13.170] (WW) AMDGPU(0): No outputs definitely connected, trying again...   
   [    13.170] (WW) AMDGPU(0): Unable to find connected outputs - setting   
   1024x768 initial framebuffer   
   [    13.170] (II) AMDGPU(0): mem size init: gart size :1f0bb8000 vram size:   
   s:fefd0000 visible:fad0000   
   [    13.170] (==) AMDGPU(0): DPI set to (96, 96)   
   [    13.170] (==) AMDGPU(0): Using gamma correction (1.0, 1.0, 1.0)   
   [    13.170] (II) Loading sub module "ramdac"   
   [    13.170] (II) LoadModule: "ramdac"   
   [    13.170] (II) Module "ramdac" already built-in   
   [    13.170] (EE) AMDGPU(0): No modes.   
   [    13.171] (II) UnloadModule: "amdgpu"   
   [    13.171] (II) UnloadSubModule: "glamoregl"   
   [    13.171] (II) Unloading glamoregl   
   [    13.171] (EE) Screen(s) found, but none have a usable configuration.   
   [    13.171] (EE)   
   Fatal server error:   
   [    13.171] (EE) no screens found(EE)   
   [    13.171] (EE)   
   ---   
   Full log: https://paste.debian.net/hidden/6f585df9 (expires: 2026-05-22   
   09:39:21 UTC+0)   
      
      
   Manual bisect results:   
      
   - 6.12.63+deb13-amd64 --> GOOD   
   - 6.16.7+deb14-amd64  --> GOOD   
   - 6.17.13+deb13-amd64 --> GOOD   
   - 6.18.5+deb13-amd64  --> BAD   
      
   Removing the paramameter 'amdgpu.dc=0' does bring back Xorg to a working state.   
   However, this should not break Xorg at all. Currently I need this parameter   
   such that   
   adjusting the brightness is possible using the 'ddcutil' application.   
      
      
      
   -- Package-specific info:   
   ** Kernel log: boot messages should be attached   
      
   ** Model information   
   sys_vendor: Gigabyte Technology Co., Ltd.   
   product_name: Z87-HD3   
   product_version: To be filled by O.E.M.   
   chassis_vendor: Gigabyte Technology Co., Ltd.   
   chassis_version: To Be Filled By O.E.M.   
   bios_vendor: American Megatrends Inc.   
   bios_version: F8   
   board_vendor: Gigabyte Technology Co., Ltd.   
   board_name: Z87-HD3   
   board_version: To be filled by O.E.M.   
      
   ** Configuration for modprobe:   
   blacklist microcode   
   blacklist arkfb   
   blacklist aty128fb   
   blacklist atyfb   
   blacklist radeonfb   
   blacklist cirrusfb   
   blacklist cyber2000fb   
   blacklist kyrofb   
   blacklist matroxfb_base   
   blacklist mb862xxfb   
   blacklist neofb   
   blacklist pm2fb   
   blacklist pm3fb   
   blacklist s3fb   
   blacklist savagefb   
   blacklist sisfb   
   blacklist tdfxfb   
   blacklist tridentfb   
   blacklist vt8623fb   
   blacklist microcode   
   options snd_pcsp index=-2   
   options cx88_alsa index=-2   
   options snd_atiixp_modem index=-2   
   options snd_intel8x0m index=-2   
   options snd_via82xx_modem index=-2   
   options md_mod start_ro=1   
   options bonding max_bonds=0   
   options dummy numdummies=0   
   options ifb numifbs=0   
      
   ** PCI devices:   
   00:16.0 Communication controller [0780]: Intel Corporation 8 Series/C220   
   Series Chipset Family MEI Controller #1 [8086:8c3a] (rev 04)   
   	Subsystem: Gigabyte Technology Co., Ltd Device [1458:1c3a]   
   	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping-   
   SERR- FastB2B- DisINTx+   
   	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- SERR-    
   	Kernel driver in use: mei_me   
   	Kernel modules: mei_me   
      
   00:1c.0 PCI bridge [0604]: Intel Corporation 8 Series/C220 Series Chipset   
   Family PCI Express Root Port #1 [8086:8c10] (rev d5) (prog-if 00 [Normal   
   decode])   
   	Subsystem: Gigabyte Technology Co., Ltd Device [1458:5001]   
   	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping-   
   SERR- FastB2B- DisINTx+   
   	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- SERR- TAbort- Reset- FastB2B-   
   		PriDiscTmr- SecDiscTmr- DiscTmrStat- DiscTmrSERREn-   
   	Capabilities:    
   	Kernel driver in use: pcieport   
   	Kernel modules: shpchp   
      
   00:1c.2 PCI bridge [0604]: Intel Corporation 8 Series/C220 Series Chipset   
   Family PCI Express Root Port #3 [8086:8c14] (rev d5) (prog-if 00 [Normal   
   decode])   
   	Subsystem: Gigabyte Technology Co., Ltd Device [1458:5001]   
   	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping-   
   SERR- FastB2B- DisINTx+   
   	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- SERR-