[Bug 211807] [drm:drm_dp_mst_dpcd_read] *ERROR* mstb 000000004e6288dd port 3: DPCD read on addr 0x60 for 1 bytes NAKed

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=211807

Fiona Buckner (pheonix991@gmail.com) changed:

           What    |Removed                     |Added
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                 CC|                            |pheonix991@gmail.com

--- Comment #21 from Fiona Buckner (pheonix991@gmail.com) ---
Seeing this on Ubuntu 22.04 pre-release. Ubuntu Kernel 5.15.0-23-generic.

> # dmesg | grep i915
> [    1.776895] i915 0000:00:02.0: [drm] VT-d active for gfx access
> [    1.776899] fb0: switching to i915 from EFI VGA
> [    1.776936] i915 0000:00:02.0: vgaarb: deactivate vga console
> [    1.780003] i915 0000:00:02.0: vgaarb: changed VGA decodes:
> olddecodes=io+mem,decodes=io+mem:owns=io+mem
> [    1.780279] i915 0000:00:02.0: [drm] Finished loading DMC firmware
> i915/kbl_dmc_ver1_04.bin (v1.4)
> [    2.675796] i915 0000:00:02.0: [drm] [ENCODER:113:DDI C/PHY C] is
> disabled/in DSI mode with an ungated DDI clock, gate it
> [    2.681117] i915 0000:00:02.0: [drm] [ENCODER:120:DDI D/PHY D] is
> disabled/in DSI mode with an ungated DDI clock, gate it
> [    3.015399] [drm] Initialized i915 1.6.0 20201103 for 0000:00:02.0 on
> minor 0
> [    3.068397] fbcon: i915drmfb (fb0) is primary device
> [    3.427857] i915 0000:00:02.0: [drm] fb0: i915drmfb frame buffer device
> [   25.814835] snd_hda_intel 0000:00:1f.3: bound 0000:00:02.0 (ops
> i915_audio_component_bind_ops [i915])
> [   26.218387] mei_hdcp 0000:00:16.0-b638ab7e-94e2-4ea2-a552-d1c54b627f04:
> bound 0000:00:02.0 (ops i915_hdcp_component_ops [i915])
> [   52.090727] mei_hdcp 0000:00:16.0-b638ab7e-94e2-4ea2-a552-d1c54b627f04:
> bound 0000:00:02.0 (ops i915_hdcp_component_ops [i915])
> [   84.800055] i915 0000:00:02.0: [drm] *ERROR* mstb 000000000a940675 port 2:
> DPCD read on addr 0x4b0 for 1 bytes NAKed
> [   84.811156] i915 0000:00:02.0: [drm] *ERROR* mstb 000000000a940675 port 3:
> DPCD read on addr 0x4b0 for 1 bytes NAKed
> [ 4814.933704] audit: type=1400 audit(1649342645.891:72): apparmor="DENIED"
> operation="open" profile="snap.chromium.chromium"
> name="/proc/sys/dev/i915/perf_stream_paranoid" pid=44648 comm="chrome"
> requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
> [ 7139.378349] i915 0000:00:02.0: [drm] *ERROR* mstb 000000000a940675 port 2:
> DPCD read on addr 0x4b0 for 1 bytes NAKed
> [ 7139.388678] i915 0000:00:02.0: [drm] *ERROR* mstb 000000000a940675 port 3:
> DPCD read on addr 0x4b0 for 1 bytes NAKed

Dell 
CPU: Intel® Core™ i7-9750H CPU @ 2.60GHz × 12 
GPU: Quadro T1000/PCIe/SSE2 / Quadro T1000/PCIe/SSE2
(forcing the Nvidia gpu through Nvidia Optimus because the Intel igpu isn't
enough for dual 4k monitors)
Dell WD19TB dock connected to the USBC Thunderbolt port.
2x HP z27 monitors. One connected to the USBC port on the dock, the other to
the Display Port.

Researching this error, I found this thread:
https://lists.freedesktop.org/archives/dri-devel/2022-February/342776.html

> This is normal (although not great TBH, I'm not sure we should be printing an
> error message for that), it's the result of fwupd trying to probe the MST hub
> to see if it's a specific Dell dock that can receive updates over DP aux, but
> it's not smart enough to know it doesn't need to poke the DP aux ranges of
> downstream branches or non-MST ports in general.
> Would definitely accept patches to make this a non-error, or at least make
> this a non-error when the read/writes come from userspace
- Lyude Paul

It might be good to speak with Lyude about it as she might be the expert on it.
 I hope this helps.

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