Connecting to Monitor without EDID

cl_swim · 06-16-2023, 02:15 PM

Hello,

We're working with an ARM-based SoC without any display outputs, running Ubuntu 20.04. We need to connect a custom touch display via HDMI with a displaylink USB adapter.
Now the problem with that custom touch display is, it does not store any display information and therefore won't send anything over DDC.

We contacted the manufacturer of the display and got a testing model which does report EDID information.
Using the adapter we were able to connect to the testing model (working file) and grab the .edid file from /var/log/displaylink.

I was trying to connect the non-EDID display by using libevdi:
- getting the displaylink card with evdi_open()
- passing the content of the .edid file
- calling evdi_connect() to signal a connection to the linux drm

Unfortunately the drm refuses the connection. syslog tells me the following:

Code:

[  877.797540] evdi: [I] (card1) Connector state: connected
[  877.797577] Raw EDID:
[  877.797589]   00 00 00 00 08 60 29 01 5c 34 01 00 01 00 00 00
[  877.797596]   01 19 01 03 80 00 00 00 0a 00 00 00 00 00 00 00
[  877.797603]   00 00 00 00 00 00 01 01 01 01 01 01 01 01 01 01
[  877.797610]   01 01 01 01 01 01 aa 0a 20 42 30 e0 2c 10 10 0a
[  877.797617]   51 04 20 e0 31 00 00 18 00 00 00 fc 00 48 44 4d
[  877.797624]   49 20 44 49 53 50 4c 41 59 0a 00 00 00 10 00 00
[  877.797631]   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10
[  877.797638]   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 24
[  877.797651] evdi evdi.0: [drm] DVI-I-1: EDID invalid.
[  877.797658] evdi: [I] (card1) Edid property set
[  877.980921] evdi: [I] (card1) Notifying mode changed: 800x600@60; bpp 32; pixel format XR24 little-endian (0x34325258)
[  877.980957] evdi: [I] (card1) Notifying display power state: on
[  888.080581] [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CRTC:33:crtc-0] flip_done timed out

Is the EDID file the problem? How can it be invalid, if it comes from a display, that's working fine?
Is the problem something else? I am new to libevdi. If there is a way for me to quickly verify, if I can draw anything on the screen, that would be helpful.

Thanks in advance.

06-16-2023, 02:15 PM	#1
cl_swim Junior Member Join Date: Jun 2023 Posts: 1	Connecting to Monitor without EDID Hello, We're working with an ARM-based SoC without any display outputs, running Ubuntu 20.04. We need to connect a custom touch display via HDMI with a displaylink USB adapter. Now the problem with that custom touch display is, it does not store any display information and therefore won't send anything over DDC. We contacted the manufacturer of the display and got a testing model which does report EDID information. Using the adapter we were able to connect to the testing model (working file) and grab the .edid file from /var/log/displaylink. I was trying to connect the non-EDID display by using libevdi: - getting the displaylink card with evdi_open() - passing the content of the .edid file - calling evdi_connect() to signal a connection to the linux drm Unfortunately the drm refuses the connection. syslog tells me the following: Code: [ 877.797540] evdi: [I] (card1) Connector state: connected [ 877.797577] Raw EDID: [ 877.797589] 00 00 00 00 08 60 29 01 5c 34 01 00 01 00 00 00 [ 877.797596] 01 19 01 03 80 00 00 00 0a 00 00 00 00 00 00 00 [ 877.797603] 00 00 00 00 00 00 01 01 01 01 01 01 01 01 01 01 [ 877.797610] 01 01 01 01 01 01 aa 0a 20 42 30 e0 2c 10 10 0a [ 877.797617] 51 04 20 e0 31 00 00 18 00 00 00 fc 00 48 44 4d [ 877.797624] 49 20 44 49 53 50 4c 41 59 0a 00 00 00 10 00 00 [ 877.797631] 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 [ 877.797638] 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 24 [ 877.797651] evdi evdi.0: [drm] DVI-I-1: EDID invalid. [ 877.797658] evdi: [I] (card1) Edid property set [ 877.980921] evdi: [I] (card1) Notifying mode changed: 800x600@60; bpp 32; pixel format XR24 little-endian (0x34325258) [ 877.980957] evdi: [I] (card1) Notifying display power state: on [ 888.080581] [drm:drm_atomic_helper_wait_for_dependencies] ERROR [CRTC:33:crtc-0] flip_done timed out Is the EDID file the problem? How can it be invalid, if it comes from a display, that's working fine? Is the problem something else? I am new to libevdi. If there is a way for me to quickly verify, if I can draw anything on the screen, that would be helpful. Thanks in advance.