Bug 207595 - [amdgpu] Displayport MST not functional on AMD Stoney
Summary: [amdgpu] Displayport MST not functional on AMD Stoney
Status: NEW
Alias: None
Product: Drivers
Classification: Unclassified
Component: Video(DRI - non Intel) (show other bugs)
Hardware: All Linux
: P1 normal
Assignee: drivers_video-dri
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-05-06 07:58 UTC by Johannes Braun
Modified: 2020-05-11 12:48 UTC (History)
1 user (show)

See Also:
Kernel Version: 5.4.28, 5.4.36
Tree: Mainline
Regression: No


Attachments
5.4.28: lspci output of Lenovo 14w notebook with stoney gpu (26.35 KB, text/plain)
2020-05-06 07:58 UTC, Johannes Braun
Details
5.4.28: Kernel log with connected display (187.14 KB, text/plain)
2020-05-06 07:59 UTC, Johannes Braun
Details
5.4.28: kernel config (187.14 KB, text/plain)
2020-05-06 07:59 UTC, Johannes Braun
Details
5.4.36: kernel config (187.14 KB, text/plain)
2020-05-06 08:04 UTC, Johannes Braun
Details
5.4.36: lspci output of Lenovo 14w notebook with stoney gpu (26.35 KB, text/plain)
2020-05-06 08:05 UTC, Johannes Braun
Details
5.4.36: Kernel log with connected display (64.17 KB, text/plain)
2020-05-06 08:06 UTC, Johannes Braun
Details

Description Johannes Braun 2020-05-06 07:58:13 UTC
Created attachment 288939 [details]
5.4.28: lspci output of Lenovo 14w notebook with stoney gpu

Hello,

I do have some issues running a Lenovo 14w notebook in a multi monitor setup. The displays are connected as followed:

[Lenovo 14w]--(USB-C)-->[Dell U2719DC]--(Display Port)-->[Some other display]

The second display is not connected directly to the notebook. This display is connected to the monitor output of the Dell display. The Dell display is configured to use MST and this setup was successfully validated with a Windows 10 installation.

When I plug the Dell 2719DC with the daisy chained monitor via USB-C to the notebook, the screens are staying black and I get crash of the amdgpu driver in dmesg. Kernel logs (5.4.28 and 5.4.36) are attached.

My system is currently based on kernel 5.4.28. But I did checked also the latest kernel version in the 5.4 LTS tree which was 5.4.36. The same error is reproducable under Ubuntu 20.04 which is based on kernel 5.4.0.

If MST is disabled in the Dell 2719DC, it works as expected. My intenal notebook screen is expanded with the USB-C connected Dell U2719DC. And the third monitor is in clone mode with the Dell U2719DC.

Thank you for reading and kind regards,
Johannes Braun
Comment 1 Johannes Braun 2020-05-06 07:59:07 UTC
Created attachment 288941 [details]
5.4.28: Kernel log with connected display
Comment 2 Johannes Braun 2020-05-06 07:59:39 UTC
Created attachment 288943 [details]
5.4.28: kernel config
Comment 3 Johannes Braun 2020-05-06 08:04:13 UTC
Created attachment 288945 [details]
5.4.36: kernel config
Comment 4 Johannes Braun 2020-05-06 08:05:34 UTC
Created attachment 288947 [details]
5.4.36: lspci output of Lenovo 14w notebook with stoney gpu
Comment 5 Johannes Braun 2020-05-06 08:06:18 UTC
Created attachment 288949 [details]
5.4.36: Kernel log with connected display
Comment 6 Alex Deucher 2020-05-08 15:57:02 UTC
Are you trying to use more than two total displays (including the laptop panel)?  Stoney only has two display controllers so it can only driver a maximum of two displays.
Comment 7 Johannes Braun 2020-05-08 19:56:27 UTC
Yes, the plan was to use three displays in total. I was not aware that this is not possible with Stoney. Thank you for the clarification.
Comment 8 Johannes Braun 2020-05-11 11:40:57 UTC
Is there a way to ask the amdgpu driver how much displays are supported, e.g. via a parameter in userspace?
Comment 9 Alex Deucher 2020-05-11 12:45:44 UTC
You can ask any KMS driver via the drmModeGetResources() function call in libdrm.
Comment 10 Alex Deucher 2020-05-11 12:48:17 UTC
If using X, you can also use `xrandr --verbose` to see number of crtcs.

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