Arch Linux

stefabat

Member

Registered: 2020-04-21

Posts: 8

Amdgpu no signal to external USB-C monitor

Hello,

Before Christmas my laptop (thinkpad z13 gen2) worked without issues when connecting to an external USB-C monitor (Dell C2722DE), which also has a USB hub and charges my laptop. I used during the past two weeks another external monitor (I don't have the details of that monitor, but it was also connected via USB-C, plus usb hub and charged my laptop), which worked also fine. Now I am back to my Dell monitor and while charging and usb hub work, the monitor does not receive the signal and I can't tell whether it is even detected.

I am using GNOME and I can see in the LOGS app the following when I connect the monitor:

amdgpu 0000:c3:00.0: [drm] *ERROR* LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.

and

amdgpu 0000:c3:00.0: [drm] *ERROR* lttpr_caps phy_repeater_cnt is 0x0, forcing it to 0x80.

I tried to downgrade my kernel to 6.17 without change. I tried to downgrade the linux-firmware-amdgpu to the second-to-last version, again no difference.
I don't know whether I updated my system while I was using the other monitor, therefore I don't know whether an update broke the functionality.
I am on wayland, I have no Xorg even installed.

stefabat

Member

Registered: 2020-04-21

Posts: 8

Re: Amdgpu no signal to external USB-C monitor

I can see that I did a big system update on December 19th, and a few others in the following week, so many packages have changed, both relating to the kernel, and to the gpu.
I also tried another screen that is thunderbolt 4 and it also doesn't work, though with different errors and I can see that the charging keeps getting connected and disconnected, while the screen is just always dark:

thunderbolt 1-2: failed to initialize port 1
hub 7-1:1.0: config failed, can't get hub status (err -5)
usb 7-1: Failed to suspend device, error -32
usb 7-1: can't set config #1, error -71

So maybe I need to update the firmware of my laptop?
I also realized that my current screen that was working before Christmas uses a USB-C 3,2 Gen 1 Upstream (DisplayPort 1.4-Modus / Spannungsversorgung von bis zu 90 W) connection, while the one I had over Christmas was thunderbolt 3, while the one I just tried is thunderbolt 4.

So, not sure all of them have the same problem?

seth

Member

From: Won't reply 2 private help req

Registered: 2012-09-03

Posts: 75,838

Re: Amdgpu no signal to external USB-C monitor

I can see that I did a big system update on December 19th

To rule out any kind of HW issue:
https://wiki.archlinux.org/title/Arch_L … cific_date (to the date of the last update *before* Dec/19th!)

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mrjones-plip

Member

Registered: Today

Posts: 1

Re: Amdgpu no signal to external USB-C monitor

I was having this same exact error.  Frustratingly, changing USBC cables fixed this.  I tested with two travel monitors on my laptop and they both exhibited the same error on 2 cables, but a 3rd cable was successful with them both.  Interestingly, one monitor would cause the errors to repeat every ~1 seconds, causing the computer to freeze for up to  ~1 second each time, while the other just showed the error once.

the unknown error and GET_CABLE_PROPERTY failed showed up for good and bad cables alike :shrug:

[  962.811539] ucsi_acpi USBC000:00: unknown error 0
[  962.811556] ucsi_acpi USBC000:00: GET_CABLE_PROPERTY failed (-5)
[  963.701856] amdgpu 0000:c1:00.0: [drm] *ERROR* lttpr_caps phy_repeater_cnt is 0x0, forcing it to 0x80.
[  963.701867] amdgpu 0000:c1:00.0: [drm] *ERROR* LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.
[  966.854359] amdgpu 0000:c1:00.0: [drm] *ERROR* lttpr_caps phy_repeater_cnt is 0x0, forcing it to 0x80.
[  966.854369] amdgpu 0000:c1:00.0: [drm] *ERROR* LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.
[  967.954155] amdgpu 0000:c1:00.0: [drm] *ERROR* lttpr_caps phy_repeater_cnt is 0x0, forcing it to 0x80.
[  967.954166] amdgpu 0000:c1:00.0: [drm] *ERROR* LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.
[  971.255198] amdgpu 0000:c1:00.0: [drm] *ERROR* lttpr_caps phy_repeater_cnt is 0x0, forcing it to 0x80.
[  971.255205] amdgpu 0000:c1:00.0: [drm] *ERROR* LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.
[  972.305540] amdgpu 0000:c1:00.0: [drm] *ERROR* lttpr_caps phy_repeater_cnt is 0x0, forcing it to 0x80.
[  972.305551] amdgpu 0000:c1:00.0: [drm] *ERROR* LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.