On Mon, 26 Jan 2026, Atharva Tiwari <[email protected]> wrote: >> Rendering and display are quite separate in the hardware and in the >> driver. Perhaps you do not mean "rendering" here? Perhaps it can be used >> for rendering but not display? > > Yeah, it can be used for rendering but not display, sorry for the wording. > >> Okay, so perhaps there's no eDP connected. But what about the other >> connectors on the iGPU? What about everything else in the display >> hardware? > > You cant use the iGPU to drive the display on any hardware (including > external displays). > >> If you can figure out that it's specifically link training that fails (a >> dmesg would be useful to show this) there clearly is display hardware, >> right? > > As said the iGPU cant drive the display on all monitors (even on macOS), but > still heres the dmesg before this patch: > > [ 5.095489] i915 0000:00:02.0: [drm] Found cometlake (device ID 9bc8) > integrated display version 9.00 stepping N/A > [ 5.096061] i915 0000:00:02.0: [drm] VT-d active for gfx access > [ 5.096102] i915 0000:00:02.0: [drm] Using Transparent Hugepages > [ 5.099214] i915 0000:00:02.0: Invalid PCI ROM header signature: expecting > 0xaa55, got 0xffff > [ 5.099217] i915 0000:00:02.0: [drm] Failed to find VBIOS tables (VBT) > [ 5.099324] i915 0000:00:02.0: vgaarb: VGA decodes changed: > olddecodes=io+mem,decodes=none:owns=io+mem > [ 5.100960] i915 0000:00:02.0: [drm] Finished loading DMC firmware > i915/kbl_dmc_ver1_04.bin (v1.4) > [ 5.832214] i915 0000:00:02.0: [drm] [ENCODER:105:DDI A/PHY A] failed to > retrieve link info, disabling eDP > [ 5.835756] i915 0000:00:02.0: [drm] Registered 3 planes with drm panic > [ 6.428455] i915 0000:00:02.0: [drm] Cannot find any crtc or sizes > [ 6.722404] i915 0000:00:02.0: [drm] Cannot find any crtc or sizes > >> There's at least three levels where this could be handled, depending on >> details: >> >> - Display probe (the patch at hand). Assumes there's no display >> hardware, at all. The driver doesn't touch the hardware, which >> continues to consume power, it's not put in low power states. Not >> optimal if there actually is display hardware. >> >> - Display disable. See intel_display_device_enabled(). The driver takes >> over the hardware, puts it to sleep, but prevents all connectors from >> being connected.
At a glance, this seems like the appropriate level. What if you drop patch 2 and supply i915.disable_display=1 module parameter? Or return false from intel_display_device_enabled(). BR, Jani. >> >> - eDP disable. Add a quirk somewhere to enforce eDP is disconnected, but >> other connectors can be used. > > The main reason I sent this patch is that after i915 trys to probe the > display, > the dGPU (amdgpu) is no longer able to detect the internal display, > resulting in a black screen. > >> It would be quite useful to indicate the PCI ID of the device in >> question. > > 00:02.0 VGA compatible controller [0300]: Intel Corporation CometLake-S GT2 > [UHD Graphics 630] [8086:9bc8] (rev 03) (prog-if 00 [VGA controller]) > Subsystem: Apple Inc. CometLake-S GT2 [UHD Graphics 630] [106b:ffff] -- Jani Nikula, Intel
