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i5-1135G7 Display flickering USB-C to DP external 4K HiDPI and FIFO underrun

Issue

Display starts flickering some minutes after boot and continues to flicker randomly - sometimes several times every 5 seconds. At the first time this happens after boot, I always see [drm] *ERROR* CPU pipe A FIFO underrun inside the logs exactly at the moment when this happens.

intel_idle.max_cstate=4 or even lower does not help in my case.

dmesg.log

System

Lenovo ThinkPad T14 Gen. 2 Intel with an LG MU67 4K monitor connected via an USB-C to DP cable running at 4K HiDPI.

System:    Kernel: 5.13.0-22-generic x86_64 bits: 64 compiler: N/A Desktop: Cinnamon 5.0.7
           Distro: Linux Mint 20.2 Uma base: Ubuntu 20.04 focal
Machine:   Type: Laptop System: LENOVO product: 20W0003AGE v: ThinkPad T14 Gen 2i serial: <filter>
           Mobo: LENOVO model: 20W0003AGE v: SDK0J40697 WIN serial: <filter> UEFI: LENOVO
           v: N34ET44W (1.44 ) date: 10/08/2021
Battery:   ID-1: BAT0 charge: 52.4 Wh condition: 52.8/50.5 Wh (105%) model: SMP 5B10W51827
           status: Charging
CPU:       Topology: Quad Core model: 11th Gen Intel Core i5-1135G7 bits: 64 type: MT MCP
           arch: Tiger Lake rev: 1 L2 cache: 8192 KiB
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 38707
           Speed: 882 MHz min/max: 400/4200 MHz Core speeds (MHz): 1: 882 2: 708 3: 638 4: 939 5: 1062
           6: 930 7: 703 8: 1096
Graphics:  Device-1: Intel vendor: Lenovo driver: i915 v: kernel bus ID: 00:02.0
           Display: x11 server: X.Org 1.20.11 driver: modesetting unloaded: fbdev,vesa
           resolution: 3840x2160~60Hz
           OpenGL: renderer: llvmpipe (LLVM 12.0.0 256 bits) v: 4.5 Mesa 21.0.3 direct render: Yes
Audio:     Device-1: Intel vendor: Lenovo driver: sof-audio-pci-intel-tgl bus ID: 00:1f.3
           Sound Server: ALSA v: k5.13.0-22-generic
Network:   Device-1: Intel Ethernet I219-V vendor: Lenovo driver: e1000e v: kernel port: efa0
           bus ID: 00:1f.6
           IF: enp0s31f6 state: down mac: <filter>
           Device-2: Intel driver: iwlwifi v: kernel port: efa0 bus ID: 09:00.0
           IF: wlp9s0 state: up mac: <filter>
           Device-3: Realtek RTL8153 Gigabit Ethernet Adapter type: USB driver: r8152 bus ID: 2-2.4:4
           IF: enxa0cec8e26e99 state: up speed: 1000 Mbps duplex: full mac: <filter>
           IF-ID-1: br-354e8e9bc4dc state: up speed: 10000 Mbps duplex: unknown mac: <filter>
           IF-ID-2: br-68823ea6d343 state: down mac: <filter>
           IF-ID-3: br-9e79b759176e state: up speed: 10000 Mbps duplex: unknown mac: <filter>
           IF-ID-4: docker0 state: down mac: <filter>
           IF-ID-5: vethba96c05 state: up speed: 10000 Mbps duplex: full mac: <filter>
           IF-ID-6: vethe7dfd4c state: up speed: 10000 Mbps duplex: full mac: <filter>
Drives:    Local Storage: total: 476.94 GiB used: 99.53 GiB (20.9%)
           ID-1: /dev/nvme0n1 vendor: SK Hynix model: HFS512GDE9X081N size: 476.94 GiB
Partition: ID-1: / size: 466.30 GiB used: 99.27 GiB (21.3%) fs: ext4 dev: /dev/dm-1
           ID-2: /boot size: 704.5 MiB used: 238.1 MiB (33.8%) fs: ext4 dev: /dev/nvme0n1p2
           ID-3: swap-1 size: 980.0 MiB used: 0 KiB (0.0%) fs: swap dev: /dev/dm-2
Sensors:   System Temperatures: cpu: 47.0 C mobo: N/A
           Fan Speeds (RPM): fan-1: 0
Info:      Processes: 382 Uptime: 3m Memory: 15.36 GiB used: 1.91 GiB (12.4%) Init: systemd
           runlevel: 5 Compilers: gcc: 9.3.0 Shell: zsh v: 5.8 inxi: 3.0.38

(Maybe) similar issues

/cc @vsyrjala

Edited by binarious
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