Comment 3 for bug 2064370

Ok, running some tests.

First thing is that with fKMS overlay, right on boot (even before the kernel started) I can see these messages on the serial console:

RPi: BOOTLOADER release VERSION:0b7b6f28 DATE: 2024/04/17 TIME: 13:51:36
BOOTMODE: 0x06 partition 0 build-ts BUILD_TIMESTAMP=1713358296 serial a0940f46 boardrev b03111 stc
(lots of lines removed)
Boot mode: USB-MSD (04) order e
HDMI0 edid block 0 offset 0
00ffffffffffff0049f7000000000000
011a0103800000000ad7a5a2594a9624
145054afce0081c00101010101010101
0101010101017f2156aa51001e30468f
33003f432100001ea91a00a050001630
3020370020560000001a000000fd0032
4c1e5010000a202020202020000000fc
004141410a20202020202020200a016f
HDMI0 edid block 1 offset 128
020323744f109f140504131216111503
0702060123090f038301000066030c00
100080011d00bc52d01e20b8285540c4
8e2100001e011d80d0721c1620102c25
80c48e2100009e8c0ad08a20e02d1010
3e9600138e210000188c0ad090204031
200c405500138e210000180000000000
0000000000000000000000000000009d
HDMI0: best-mode 1 (limit 1) 1280x720 60 Hz CEA modes fe007f80000000000000000000000000 extensions 1
USB2[1] 400202e1 connected

If I switch to the KMS overlay, the message is exactly the same, so it means the EDID is accessible from the monitor in either case. I compared both outputs and they are the same.

But with KMS, as expected, the monitor went blank again by the end of the boot messages.

Another interesting thing is that I *could* dump edid even with the KMS overlay right after boot, once. When I tried again, it did not work anymore, saying it was empty:

ubuntu@ubuntu:~$ edid-decode /sys/class/drm/card0-HDMI-A-1/edid
edid-decode (hex):

00 ff ff ff ff ff ff 00 49 f7 00 00 00 00 00 00
01 1a 01 03 80 00 00 00 0a d7 a5 a2 59 4a 96 24
14 50 54 af ce 00 81 c0 01 01 01 01 01 01 01 01
01 01 01 01 01 01 7f 21 56 aa 51 00 1e 30 46 8f
33 00 3f 43 21 00 00 1e a9 1a 00 a0 50 00 16 30
30 20 37 00 20 56 00 00 00 1a 00 00 00 fd 00 32
4c 1e 50 10 00 0a 20 20 20 20 20 20 00 00 00 fc
00 41 41 41 0a 20 20 20 20 20 20 20 20 0a 01 6f

02 03 23 74 4f 10 9f 14 05 04 13 12 16 11 15 03
07 02 06 01 23 09 0f 03 83 01 00 00 66 03 0c 00
10 00 80 01 1d 00 bc 52 d0 1e 20 b8 28 55 40 c4
8e 21 00 00 1e 01 1d 80 d0 72 1c 16 20 10 2c 25
80 c4 8e 21 00 00 9e 8c 0a d0 8a 20 e0 2d 10 10
3e 96 00 13 8e 21 00 00 18 8c 0a d0 90 20 40 31
20 0c 40 55 00 13 8e 21 00 00 18 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 9d

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

Block 0, Base EDID:
  EDID Structure Version & Revision: 1.3
  Vendor & Product Identification:
    Manufacturer: ROW
    Model: 0
    Made in: week 1 of 2016
  Basic Display Parameters & Features:
    Digital display
    Image size is variable
    Gamma: 1.00
    RGB color display
    First detailed timing is the preferred timing
  Color Characteristics:
    Red : 0.6357, 0.3486
    Green: 0.2900, 0.5888
    Blue : 0.1425, 0.0800
    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 0x05: 640x480 72.808802 Hz 4:3 37.861 kHz 31.500000 MHz
    DMT 0x06: 640x480 75.000000 Hz 4:3 37.500 kHz 31.500000 MHz
    DMT 0x08: 800x600 56.250000 Hz 4:3 35.156 kHz 36.000000 MHz
    DMT 0x09: 800x600 60.316541 Hz 4:3 37.879 kHz 40.000000 MHz
    DMT 0x0a: 800x600 72.187572 Hz 4:3 48.077 kHz 50.000000 MHz
    DMT 0x0b: 800x600 75.000000 Hz 4:3 46.875 kHz 49.500000 MHz
    DMT 0x10: 1024x768 60.003840 Hz 4:3 48.363 kHz 65.000000 MHz
    DMT 0x11: 1024x768 70.069359 Hz 4:3 56.476 kHz 75.000000 MHz
    DMT 0x12: 1024x768 75.028582 Hz 4:3 60.023 kHz 78.750000 MHz
  Standard Timings:
    DMT 0x55: 1280x720 60.000000 Hz 16:9 45.000 kHz 74.250000 MHz
  Detailed Timing Descriptors:
    DTD 1: 1366x768 59.964364 Hz 683:384 47.852 kHz 85.750000 MHz (575 mm x 323 mm)
                 Hfront 70 Hsync 143 Hback 213 Hpol P
                 Vfront 3 Vsync 3 Vback 24 Vpol P
    DTD 2: 1280x768 59.994726 Hz 5:3 47.396 kHz 68.250000 MHz (32 mm x 86 mm)
                 Hfront 48 Hsync 32 Hback 80 Hpol P
                 Vfront 3 Vsync 7 Vback 12 Vpol N
    Display Range Limits:
      Monitor ranges (GTF): 50-76 Hz V, 30-80 kHz H, max dotclock 160 MHz
    Display Product Name: 'AAA'
  Extension blocks: 1
Checksum: 0x6f

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

Block 1, CTA-861 Extension Block:
  Revision: 3
  Basic audio support
  Supports YCbCr 4:4:4
  Supports YCbCr 4:2:2
  Native detailed modes: 4
  Video Data Block:
    VIC 16: 1920x1080 60.000000 Hz 16:9 67.500 kHz 148.500000 MHz
    VIC 31: 1920x1080 50.000000 Hz 16:9 56.250 kHz 148.500000 MHz (native)
    VIC 20: 1920x1080i 50.000000 Hz 16:9 28.125 kHz 74.250000 MHz
    VIC 5: 1920x1080i 60.000000 Hz 16:9 33.750 kHz 74.250000 MHz
    VIC 4: 1280x720 60.000000 Hz 16:9 45.000 kHz 74.250000 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 22: 1440x576i 50.000000 Hz 16:9 15.625 kHz 27.000000 MHz
    VIC 17: 720x576 50.000000 Hz 4:3 31.250 kHz 27.000000 MHz
    VIC 21: 1440x576i 50.000000 Hz 4:3 15.625 kHz 27.000000 MHz
    VIC 3: 720x480 59.940060 Hz 16:9 31.469 kHz 27.000000 MHz
    VIC 7: 1440x480i 59.940060 Hz 16:9 15.734 kHz 27.000000 MHz
    VIC 2: 720x480 59.940060 Hz 4:3 31.469 kHz 27.000000 MHz
    VIC 6: 1440x480i 59.940060 Hz 4:3 15.734 kHz 27.000000 MHz
    VIC 1: 640x480 59.940476 Hz 4:3 31.469 kHz 25.175000 MHz
  Audio Data Block:
    Linear PCM:

ubuntu@ubuntu:~$ edid-decode /sys/class/drm/card0-HDMI-A-1/edid
EDID of '/sys/class/drm/card0-HDMI-A-1/edid' was empty.

This seems very odd.

I'm still gonna test force_hotplug and overriding edid.