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Display connected to Kensington TB4/USB4 dock results in no EDID/just 640x480 mode

Brief summary of the problem:

Monitor works correctly (all modes including native 3840x2160@60Hz) connected directly to the laptop over a Framework USB-C/HDMI adapter. Also works through the dock with Intel-based Framework and Macbook Pro M1 laptops.

On the Framework AMD 7840U laptop however, when connected through the dock the monitor is only seen at a generic(?) 640x480 resolution, with no EDID info.

Hardware description:

  • CPU: 7840U
  • GPU: 1:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Phoenix1 [1002:15bf] (rev c4)
  • System Memory: 64GB
  • Display(s): Built-in laptop panel 2256x1504@60, HP Z27 3840x2160
  • Type of Display Connection: HDMI

System information:

  • Distro name and Version: Fedora 39
  • Kernel version: 6.6.6-200.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Mon Dec 11 17:29:08 UTC 2023 x86_64 GNU/Linux
  • Custom kernel: N/A
  • AMD official driver version: N/A

How to reproduce the issue:

I can reproduce this issue 100% reliably. Tried hot- and cold-plugging in the monitor, same with the dock itself, as well as power cycling the dock.

Conversely, when connected directly through the Framework HDMI adapter, the monitor works correctly 100% of the time.

With the Intel (11 gen) laptop, the monitor works through the dock correctly virtually always. When it rarely doesn't, it either stays dark or connects at the same (I believe, been a while) 640x480 resolution. In those cases, power-cycling the dock has been able to correct the issue every time.

When connected directly on HDMI, the monitor's EDID is:

$ cat /sys/class/drm/card1/card1-DP-4/edid |edid-decode 
edid-decode (hex):

00 ff ff ff ff ff ff 00 22 0e 38 35 01 01 01 01
14 1e 01 03 80 3c 22 78 2e ee 95 a3 54 4c 99 26
0f 50 54 a1 08 00 d1 c0 a9 c0 81 c0 d1 00 b3 00
95 00 81 00 81 80 4d d0 00 a0 f0 70 3e 80 30 20
35 00 55 50 21 00 00 1a 00 00 00 fd 00 1d 3c 1c
87 3c 00 0a 20 20 20 20 20 20 00 00 00 fc 00 48
50 20 5a 32 37 0a 20 20 20 20 20 20 00 00 00 ff
00 43 4e 34 30 32 30 30 50 4d 4a 0a 20 20 01 bc

02 03 38 f1 51 61 10 04 03 02 1f 13 12 11 5f 05
14 07 06 16 15 01 23 09 07 07 83 01 00 00 6b 03
0c 00 10 00 38 3c 20 00 20 01 67 d8 5d c4 01 78
80 03 e2 0f 01 e2 00 2b a3 66 00 a0 f0 70 1f 80
30 20 35 00 55 50 21 00 00 1a 02 3a 80 18 71 38
2d 40 58 2c 45 00 55 50 21 00 00 1e 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 05

----------------

Block 0, Base EDID:
  EDID Structure Version & Revision: 1.3
  Vendor & Product Identification:
    Manufacturer: HPN
    Model: 13624
    Serial Number: 16843009
    Made in: week 20 of 2020
  Basic Display Parameters & Features:
    Digital display
    Maximum image size: 60 cm x 34 cm
    Gamma: 2.20
    DPMS levels: Off
    RGB color display
    Default (sRGB) color space is primary color space
    First detailed timing is the preferred timing
  Color Characteristics:
    Red  : 0.6396, 0.3300
    Green: 0.2998, 0.5996
    Blue : 0.1503, 0.0595
    White: 0.3134, 0.3291
  Established Timings I & II:
    IBM     :   720x400    70.081663 Hz   9:5     31.467 kHz     28.320000 MHz
    DMT 0x04:   640x480    59.940476 Hz   4:3     31.469 kHz     25.175000 MHz
    DMT 0x09:   800x600    60.316541 Hz   4:3     37.879 kHz     40.000000 MHz
    DMT 0x10:  1024x768    60.003840 Hz   4:3     48.363 kHz     65.000000 MHz
  Standard Timings:
    DMT 0x52:  1920x1080   60.000000 Hz  16:9     67.500 kHz    148.500000 MHz
    DMT 0x53:  1600x900    60.000000 Hz  16:9     60.000 kHz    108.000000 MHz (RB)
    DMT 0x55:  1280x720    60.000000 Hz  16:9     45.000 kHz     74.250000 MHz
    DMT 0x45:  1920x1200   59.884600 Hz  16:10    74.556 kHz    193.250000 MHz
    DMT 0x3a:  1680x1050   59.954250 Hz  16:10    65.290 kHz    146.250000 MHz
    DMT 0x2f:  1440x900    59.887445 Hz  16:10    55.935 kHz    106.500000 MHz
    DMT 0x1c:  1280x800    59.810326 Hz  16:10    49.702 kHz     83.500000 MHz
    DMT 0x23:  1280x1024   60.019740 Hz   5:4     63.981 kHz    108.000000 MHz
  Detailed Timing Descriptors:
    DTD 1:  3840x2160   59.996625 Hz  16:9    133.312 kHz    533.250000 MHz (597 mm x 336 mm)
                 Hfront   48 Hsync  32 Hback   80 Hpol P
                 Vfront    3 Vsync   5 Vback   54 Vpol N
    Display Range Limits:
      Monitor ranges (GTF): 29-60 Hz V, 28-135 kHz H, max dotclock 600 MHz
    Display Product Name: 'HP Z27'
    Display Product Serial Number: 'CN40200PMJ'
  Extension blocks: 1
Checksum: 0xbc

----------------

Block 1, CTA-861 Extension Block:
  Revision: 3
  Underscans IT Video Formats by default
  Basic audio support
  Supports YCbCr 4:4:4
  Supports YCbCr 4:2:2
  Native detailed modes: 1
  Video Data Block:
    VIC  97:  3840x2160   60.000000 Hz  16:9    135.000 kHz    594.000000 MHz
    VIC  16:  1920x1080   60.000000 Hz  16:9     67.500 kHz    148.500000 MHz
    VIC   4:  1280x720    60.000000 Hz  16:9     45.000 kHz     74.250000 MHz
    VIC   3:   720x480    59.940060 Hz  16:9     31.469 kHz     27.000000 MHz
    VIC   2:   720x480    59.940060 Hz   4:3     31.469 kHz     27.000000 MHz
    VIC  31:  1920x1080   50.000000 Hz  16:9     56.250 kHz    148.500000 MHz
    VIC  19:  1280x720    50.000000 Hz  16:9     37.500 kHz     74.250000 MHz
    VIC  18:   720x576    50.000000 Hz  16:9     31.250 kHz     27.000000 MHz
    VIC  17:   720x576    50.000000 Hz   4:3     31.250 kHz     27.000000 MHz
    VIC  95:  3840x2160   30.000000 Hz  16:9     67.500 kHz    297.000000 MHz
    VIC   5:  1920x1080i  60.000000 Hz  16:9     33.750 kHz     74.250000 MHz
    VIC  20:  1920x1080i  50.000000 Hz  16:9     28.125 kHz     74.250000 MHz
    VIC   7:  1440x480i   59.940060 Hz  16:9     15.734 kHz     27.000000 MHz
    VIC   6:  1440x480i   59.940060 Hz   4:3     15.734 kHz     27.000000 MHz
    VIC  22:  1440x576i   50.000000 Hz  16:9     15.625 kHz     27.000000 MHz
    VIC  21:  1440x576i   50.000000 Hz   4:3     15.625 kHz     27.000000 MHz
    VIC   1:   640x480    59.940476 Hz   4:3     31.469 kHz     25.175000 MHz
  Audio Data Block:
    Linear PCM:
      Max channels: 2
      Supported sample rates (kHz): 48 44.1 32
      Supported sample sizes (bits): 24 20 16
  Speaker Allocation Data Block:
    FL/FR - Front Left/Right
  Vendor-Specific Data Block (HDMI), OUI 00-0C-03:
    Source physical address: 1.0.0.0
    DC_36bit
    DC_30bit
    DC_Y444
    Maximum TMDS clock: 300 MHz
    Extended HDMI video details:
      HDMI VICs:
        HDMI VIC 1:  3840x2160   30.000000 Hz  16:9     67.500 kHz    297.000000 MHz
  Vendor-Specific Data Block (HDMI Forum), OUI C4-5D-D8:
    Version: 1
    Maximum TMDS Character Rate: 600 MHz
    SCDC Present
    Supports 12-bits/component Deep Color 4:2:0 Pixel Encoding
    Supports 10-bits/component Deep Color 4:2:0 Pixel Encoding
  YCbCr 4:2:0 Capability Map Data Block:
    VIC  97:  3840x2160   60.000000 Hz  16:9    135.000 kHz    594.000000 MHz
  Video Capability Data Block:
    YCbCr quantization: No Data
    RGB quantization: No Data
    PT scan behavior: Always Underscanned
    IT scan behavior: Always Underscanned
    CE scan behavior: Supports both over- and underscan
  Detailed Timing Descriptors:
    DTD 2:  3840x2160   29.980602 Hz  16:9     65.688 kHz    262.750000 MHz (597 mm x 336 mm)
                 Hfront   48 Hsync  32 Hback   80 Hpol P
                 Vfront    3 Vsync   5 Vback   23 Vpol N
    DTD 3:  1920x1080   60.000000 Hz  16:9     67.500 kHz    148.500000 MHz (597 mm x 336 mm)
                 Hfront   88 Hsync  44 Hback  148 Hpol P
                 Vfront    4 Vsync   5 Vback   36 Vpol P
Checksum: 0x05  Unused space in Extension Block: 35 bytes

When connected through the dock the EDID is empty, and the only available mode is:

$ cat /sys/class/drm/card1/card1-DP-7/modes 
640x480

This Fedora kernel seems to have simpledrm built in:

$ modinfo simpledrm
name:           simpledrm
filename:       (builtin)
license:        GPL v2
file:           drivers/gpu/drm/tiny/simpledrm
description:    DRM driver for simple-framebuffer platform devices

The specific dock is this one

$ boltctl info acd38780-0078-0160-ffff-ffffffffffff
 ● Kensington Thunderbolt 4 Docking Station
   ├─ type:          peripheral
   ├─ name:          Thunderbolt 4 Docking Station
   ├─ vendor:        Kensington
   ├─ uuid:          acd38780-0078-0160-ffff-ffffffffffff
   ├─ dbus path:     /org/freedesktop/bolt/devices/acd38780_0078_0160_ffff_ffffffffffff
   ├─ generation:    USB4
   ├─ status:        authorized
   │  ├─ domain:     a3f73804-d1db-6f64-ffff-ffffffffffff
   │  ├─ parent:     a3f73804-d1db-6f64-ffff-ffffffffffff
   │  ├─ syspath:    /sys/devices/pci0000:00/0000:00:08.3/0000:c3:00.6/domain1/1-0/1-2
   │  ├─ rx speed:   40 Gb/s = 2 lanes * 20 Gb/s
   │  ├─ tx speed:   40 Gb/s = 2 lanes * 20 Gb/s
   │  └─ authflags:  boot
   ├─ authorized:    Wed 13 Dec 2023 04:52:02 PM UTC
   ├─ connected:     Wed 13 Dec 2023 04:52:02 PM UTC
   └─ stored:        Wed 15 Nov 2023 02:47:22 AM UTC
      ├─ policy:     iommu
      └─ key:        no
Edited by Dimitris