Fix CPU pipe B FIFO underrun (screen goes black for a few seconds).

i915_pri_wm_latency.sh

#!/usr/bin/env bash

# Fix CPU pipe B FIFO underrun (screen goes black for a few seconds).
# Reference: https://gitlab.freedesktop.org/drm/intel/-/issues/5455
#
# Author: Maulik Mistry
# Please share support: https://www.paypal.com/paypalme/m1st0

# License: BSD License 2.0
# Copyright (c) 2023–2025, Maulik Mistry
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright
#       notice, this list of conditions and the following disclaimer in the
#       documentation and/or other materials provided with the distribution.
#     * Neither the name of the <organization> nor the
#       names of its contributors may be used to endorse or promote products
#       derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
# DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

# Define color codes
GREEN='\033[0;32m'
RED='\033[0;31m'
NC='\033[0m' # No Color

# Desired new values
new_values=(25 39 48 52 83 97 103 120)

# Loop through each DRI file
for file in /sys/kernel/debug/dri/*/i915_pri_wm_latency; do

    # Initial read
    initial_read=$(cat "$file")

    # Extract numerical values from the initial read
    initial_values=()
    while read -r line; do
        for part in $line; do
            if [[ $part =~ ^[0-9]+$ ]]; then
                initial_values+=("$part")
            fi
        done
    done <<< "$initial_read"

    # Set new values
    echo "${new_values[@]}" | sudo tee "$file" > /dev/null

    # Read back values
    read_back=$(cat "$file")

    # Extract only the numerical values from the read_back
    returned_values=()
    while read -r line; do
        for part in $line; do
            if [[ $part =~ ^[0-9]+$ ]]; then
                returned_values+=("$part")
            fi
        done
    done <<< "$read_back"

    # Display matches in a table format
    printf "%-10s %-10s %-10s %-10s\n" "Index" "Initial" "Set Value" "Returned Value"
    printf "%-10s %-10s %-10s %-10s\n" "-----" "-------" "----------" "--------------"

    for i in "${!new_values[@]}"; do
        # Use default if initial value is not set
        initial_value="${initial_values[i]:-0}" 
        
        printf "%-10s %-10s " "WM$i" "$initial_value"
        
        # Compare returned values with the set values
        if [[ "${returned_values[$i]}" == "${new_values[$i]}" ]]; then
            printf "${GREEN}%-10s${NC} ${GREEN}%-10s (Match)${NC}\n" "${new_values[$i]}" "${returned_values[$i]}"
        else
            printf "${RED}%-10s${NC} ${RED}%-10s (Mismatch)${NC}\n" "${new_values[$i]}" "${returned_values[$i]}"
        fi
    done

    printf "\n"

done

i915_underrun.service

[Unit]
Description=Run fix for FIFO underrun as root after KDE login
After=systemd-modules-load.service
Wants=systemd-modules-load.service

[Service]
Type=oneshot
ExecStart=/home/mistry/my_builds/i915_underrun/i915_pri_wm_latency.sh
RemainAfterExit=yes

[Install]
WantedBy=graphical.target