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'No Signal' on UHD 630, dmesg: i915 0000:00:02.0: [drm] *ERROR* crtc 51: Can't calculate constants, dotclock = 0!

On booting the system when starting X -- video signal disappears and dmesg gets some stack traces. This happens on stable and mainline kernels we have tried (list below), except on drm-tip (bisected problem-solving commit below).

  • Reproducible: always.
  • lspci: 00:02.0 VGA compatible controller: Intel Corporation CometLake-S GT2 [UHD Graphics 630] (rev 05) (prog-if 00 [VGA controller]) Subsystem: ASRock Incorporation Device 9bc5
  • CPU: Intel(R) Core(TM) i9-10900 CPU @ 2.80GHz
  • Architecture: x86_64
  • Failing kernels: 5.11.0-rc2+, 5.12.0-rc4+ (mainline), 5.11.7 (stable), 5.4.107 (stable).
  • Distribution: ALT Linux.
  • dmidecode: Manufacturer: ASRock Product Name: H570M Pro4
  • Display connectors: HDMI and Display Port (both tried).
  • Bisected first commit fixing the issue:
commit 70da7521e11939ebf2e3d2b4cd91d30d0d02e3c4 (HEAD, refs/bisect/new)
Author: Lyude Paul <lyude@redhat.com>
Date:   Tue Feb 9 15:11:09 2021 -0500

    drm/i915/gen9_bc: Add W/A for missing STRAP config on TGP PCH + CML combos
    
    Apparently the new gen9_bc platforms that Intel has introduced don't
    provide us with a STRAP config register to read from for initializing DDI
    B, C, and D detection. So, workaround this by hard-coding our strap config
    in intel_setup_outputs().
    
    Changes since v4:
    * Split this into it's own commit
    
    Cc: Matt Roper <matthew.d.roper@intel.com>
    Cc: Jani Nikula <jani.nikula@linux.intel.com>
    Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
    [originally from Tejas's work]
    Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
    Signed-off-by: Lyude Paul <lyude@redhat.com>
    Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20210209212832.1401815-5-lyude@redhat.com
---
 drivers/gpu/drm/i915/display/intel_display.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

This would be so good to get it fixed for stable kernels, or to know workaround, or, at least, to have list of commits that we should include in our distribution kernels to have them working with the card.

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