Public bug reported:
================================================================================
KERNEL BUG REPORT: UCSI USB-C PD Charging Regression on Samsung Galaxy Book4
================================================================================
Date: 2026-03-18
Reporter: Dr. Brian King
Hardware: Samsung Galaxy Book4 (NP750XGK)
OS: Ubuntu 25.10
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SUMMARY
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USB-C Power Delivery (PD) negotiation fails to reach rated charging voltage
(20V) under kernel 6.17.0-19-generic, resulting in approximately half the
expected charging wattage (~27W observed vs. 45-65W expected). The issue was
not present on the previously installed kernel 6.17.0-12-generic.
Additionally, charging speed while the system is powered off appears slower
than before the kernel update, suggesting the embedded controller (EC) charging
profile is not being properly initialized during shutdown/handoff.
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HARDWARE
--------------------------------------------------------------------------------
System: Samsung Galaxy Book4
Model: NP750XGK
Battery: SAMSUNG Electronics SR Real Battery
Design capacity: 3530 mAh
Full capacity: 3221 mAh (91.2% health, 258 cycles)
Chemistry: Li-ion
Nominal voltage: 15.4V
Charger: Samsung OEM USB-C (65W rated, 20V/3.25A)
Charging port: USB-C (UCSI, supports PD and PPS)
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KERNEL VERSIONS
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Affected: 6.17.0-19-generic (Ubuntu 25.10)
Not affected: 6.17.0-12-generic (Ubuntu 25.10, previously installed)
Kernel 6.17.0-12 was removed from the system on 2026-03-18 via apt during
routine kernel cleanup, so a direct side-by-side comparison via reboot is no
longer possible.
Kernel update to 6.17.0-19 was installed on 2026-03-16:
2026-03-16 21:11:05 status installed linux-image-6.17.0-19-generic:amd64
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PROBLEM DESCRIPTION
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Under kernel 6.17.0-19, USB-C PD negotiation settles at approximately 15.8V
instead of the expected 20V. This results in ~27W actual delivery instead of
the rated 45-65W, causing noticeably slow charging.
The UCSI power supply sysfs node reports VOLTAGE_NOW=0 and VOLTAGE_MAX=0,
indicating the kernel is not reading voltage from the PD source at all. The
charge type is reported as "Standard" rather than "Fast", confirming PD is not
being fully utilized despite the port advertising PD and PPS support.
Reloading the ucsi_acpi kernel module (modprobe -r ucsi_acpi && modprobe
ucsi_acpi) temporarily improves PD negotiation, suggesting the issue is in
UCSI module initialization rather than a permanent hardware or firmware failure.
Notably, dmesg contains zero UCSI, typec, or power delivery messages, which is
abnormal — PD negotiation events should be logged at boot.
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SYSFS DATA
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/sys/class/power_supply/ contents:
ADP1 BAT1 ucsi-source-psy-USBC000:001 ucsi-source-psy-USBC000:002
BAT1 uevent (while charging, OS running):
POWER_SUPPLY_STATUS=Charging
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CYCLE_COUNT=258
POWER_SUPPLY_VOLTAGE_MIN_DESIGN=15400000
POWER_SUPPLY_VOLTAGE_NOW=16316000 (16.3V — should be ~20V under PD)
POWER_SUPPLY_CURRENT_NOW=1668000 (1.67A)
POWER_SUPPLY_CHARGE_FULL_DESIGN=3530000
POWER_SUPPLY_CHARGE_FULL=3221000
POWER_SUPPLY_CHARGE_CONTROL_END_THRESHOLD=100
POWER_SUPPLY_MODEL_NAME=SR Real Battery
POWER_SUPPLY_MANUFACTURER=SAMSUNG Electronics
Calculated actual wattage: 16.3V x 1.67A = ~27.2W
Expected wattage: 20V x 2.25A = ~45W (minimum rated)
ucsi-source-psy-USBC000:002 uevent (active charging port):
POWER_SUPPLY_TYPE=USB
POWER_SUPPLY_CHARGE_TYPE=Standard (should be Fast)
POWER_SUPPLY_ONLINE=1
POWER_SUPPLY_VOLTAGE_MAX=0 (BUG: should report charger max
voltage)
POWER_SUPPLY_VOLTAGE_MIN=0 (BUG: should report charger min
voltage)
POWER_SUPPLY_VOLTAGE_NOW=0 (BUG: voltage not being read from PD
source)
POWER_SUPPLY_CURRENT_MAX=0 (BUG: current max not being read)
POWER_SUPPLY_CURRENT_NOW=2250000
POWER_SUPPLY_USB_TYPE=C [PD] PD_PPS (port correctly identifies PD/PPS
support)
POWER_SUPPLY_SCOPE=Device
ucsi-source-psy-USBC000:001 uevent (inactive port):
POWER_SUPPLY_ONLINE=0
ADP1/online: 1 (AC adapter correctly detected at system level)
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DMESG FINDINGS
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sudo dmesg | grep -i "ucsi|typec|pd|charger" returns NO relevant output.
This is abnormal. No UCSI initialization, PD negotiation, or typec messages
are logged at boot, suggesting the UCSI stack is initializing silently and
possibly incorrectly.
--------------------------------------------------------------------------------
STEPS TO REPRODUCE
--------------------------------------------------------------------------------
1. Install kernel 6.17.0-19-generic on Ubuntu 25.10
2. Boot system with Samsung OEM 65W USB-C charger connected
3. Check charging wattage:
/bin/cat /sys/class/power_supply/BAT1/voltage_now
/bin/cat /sys/class/power_supply/BAT1/current_now
4. Observe voltage ~15.8V instead of expected 20V
5. Check UCSI source node:
/bin/cat /sys/class/power_supply/ucsi-source-psy-USBC000:002/voltage_now
6. Observe VOLTAGE_NOW=0 (voltage not being read from PD source)
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WORKAROUND
--------------------------------------------------------------------------------
Reloading the ucsi_acpi module after boot restores partial PD negotiation:
sudo modprobe -r ucsi_acpi && sudo modprobe ucsi_acpi
This brings charging back to ~27W. It does not fully restore the expected 45W+
but is better than the initial state. The workaround must be reapplied after
each reboot.
A systemd oneshot service can automate this workaround:
[Unit]
Description=Reset UCSI ACPI for USB-C PD negotiation
After=multi-user.target
[Service]
Type=oneshot
ExecStart=/bin/sh -c 'modprobe -r ucsi_acpi && modprobe ucsi_acpi'
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target
--------------------------------------------------------------------------------
ADDITIONAL NOTES
--------------------------------------------------------------------------------
- TLP is installed (v1.8.0) but charge thresholds are not configured (end
threshold = 100%). TLP is not the cause of this issue.
- The battery reports 91.2% capacity at 258 cycles — battery health is not
a factor.
- The issue also manifests as slower-than-expected charging when the system is
powered off, suggesting EC charging profile handoff at shutdown may also be
affected by this regression.
- No UCSI-related kernel parameters have been modified.
--------------------------------------------------------------------------------
SUGGESTED BISECT RANGE
--------------------------------------------------------------------------------
Good: 6.17.0-12-generic
Bad: 6.17.0-19-generic
Subsystem: drivers/usb/typec/ucsi/
Relevant files: ucsi_acpi.c, ucsi.c, psy.c
Maintainer: Heikki Krogerus <[email protected]>
--------------------------------------------------------------------------------
CONTACT
--------------------------------------------------------------------------------
Reporter is available to provide additional diagnostic output, test patches,
or run bisect builds if needed. System runs Ubuntu 25.10 with kernel 6.17 and
is available for follow-up testing.
================================================================================
END OF REPORT
================================================================================
➜ ~ # Capture everything relevant in one shot
sudo dmesg > ~/dmesg-kernel-charging.txt
sudo dmidecode > ~/dmidecode.txt
/bin/cat /sys/class/power_supply/BAT1/uevent
/bin/cat /sys/class/power_supply/ucsi-source-psy-USBC000:002/uevent
[sudo: authenticate] Password:
DEVTYPE=power_supply
POWER_SUPPLY_NAME=BAT1
POWER_SUPPLY_TYPE=Battery
POWER_SUPPLY_STATUS=Charging
POWER_SUPPLY_PRESENT=1
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CYCLE_COUNT=258
POWER_SUPPLY_VOLTAGE_MIN_DESIGN=15400000
POWER_SUPPLY_VOLTAGE_NOW=16316000
POWER_SUPPLY_CURRENT_NOW=1668000
POWER_SUPPLY_CHARGE_FULL_DESIGN=3530000
POWER_SUPPLY_CHARGE_FULL=3221000
POWER_SUPPLY_CHARGE_NOW=1885000
POWER_SUPPLY_CHARGE_CONTROL_END_THRESHOLD=100
POWER_SUPPLY_CAPACITY=59
POWER_SUPPLY_CAPACITY_LEVEL=Normal
POWER_SUPPLY_TYPE=Battery
POWER_SUPPLY_MODEL_NAME=SR Real Battery
POWER_SUPPLY_MANUFACTURER=SAMSUNG Electronics
POWER_SUPPLY_SERIAL_NUMBER=123456789
DEVTYPE=power_supply
POWER_SUPPLY_NAME=ucsi-source-psy-USBC000:002
POWER_SUPPLY_TYPE=USB
POWER_SUPPLY_CHARGE_TYPE=Standard
POWER_SUPPLY_ONLINE=1
POWER_SUPPLY_VOLTAGE_MAX=0
POWER_SUPPLY_VOLTAGE_MIN=0
POWER_SUPPLY_VOLTAGE_NOW=0
POWER_SUPPLY_CURRENT_MAX=0
POWER_SUPPLY_CURRENT_NOW=2250000
POWER_SUPPLY_TYPE=USB
POWER_SUPPLY_USB_TYPE=C [PD] PD_PPS
POWER_SUPPLY_SCOPE=Device
➜ ~ ubuntu-bug linux
REDACTED config part /etc/cloud/cloud.cfg.d/99-installer.cfg, insufficient
permissions
REDACTED config part /etc/cloud/cloud.cfg.d/90-installer-network.cfg,
insufficient permissions
Opening in existing browser session.
➜ ~
ProblemType: Bug
DistroRelease: Ubuntu 25.10
Package: linux-image-6.17.0-19-generic 6.17.0-19.19
ProcVersionSignature: Ubuntu 6.17.0-19.19-generic 6.17.13
Uname: Linux 6.17.0-19-generic x86_64
ApportVersion: 2.33.1-0ubuntu3
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: brian 4113 F.... pipewire
brian 4134 F.... wireplumber
/dev/snd/seq: brian 4113 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Wed Mar 18 21:38:53 2026
InstallationDate: Installed on 2025-05-23 (299 days ago)
InstallationMedia: Ubuntu 25.04 "Plucky Puffin" - Release amd64 (20250415.3)
MachineType: SAMSUNG ELECTRONICS CO., LTD. 750XGK
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/usr/bin/zsh
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-6.17.0-19-generic
root=UUID=67cdc73c-425b-47f6-a88c-636207de0da4 ro quiet splash lockdown=none
resume=UUID=67cdc73c-425b-47f6-a88c-636207de0da4 resume_offset=103645184
i915.enable_dc=0 i915.enable_psr=0 i915.enable_fbc=0
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
vt.handoff=7
RelatedPackageVersions:
firmware-sof N/A
linux-firmware 20250901.git993ff19b-0ubuntu1.9
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/09/2024
dmi.bios.release: 5.27
dmi.bios.vendor: American Megatrends International, LLC.
dmi.bios.version: P02CFP.015.240409.HQ
dmi.board.asset.tag: No Asset Tag
dmi.board.name: NP750XGK-KS2US
dmi.board.vendor: SAMSUNG ELECTRONICS CO., LTD.
dmi.board.version: SAMSUNG_SW_REVISION_12345+10.0.22631
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: SAMSUNG ELECTRONICS CO., LTD.
dmi.chassis.version: N/A
dmi.modalias:
dmi:bvnAmericanMegatrendsInternational,LLC.:bvrP02CFP.015.240409.HQ:bd04/09/2024:br5.27:svnSAMSUNGELECTRONICSCO.,LTD.:pn750XGK:pvrP02CFP:rvnSAMSUNGELECTRONICSCO.,LTD.:rnNP750XGK-KS2US:rvrSAMSUNG_SW_REVISION_12345+10.0.22631:cvnSAMSUNGELECTRONICSCO.,LTD.:ct10:cvrN/A:skuSCAI-A5A5-A5A5-RPLU-PCFP:
dmi.product.family: Galaxy Book4
dmi.product.name: 750XGK
dmi.product.sku: SCAI-A5A5-A5A5-RPLU-PCFP
dmi.product.version: P02CFP
dmi.sys.vendor: SAMSUNG ELECTRONICS CO., LTD.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug questing wayland-session
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https://bugs.launchpad.net/bugs/2144850
Title:
Charging, Samsung Galaxy Book4 (NP750XGK). regression?
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