Public bug reported:
On a Lenovo ThinkPad X9-15 Gen 1 (Intel Core Ultra 7 258V, Lunar Lake,
IPU7 8086:645d, Sony IMX471 sensor), the built-in camera works through
libcamera, but frames contain short colored horizontal dashes wherever
the image changes between frames, for example when moving a hand quickly
in front of the camera. A static scene looks clean.
Analysis:
- Most full-length dashes are exactly 32 pixels wide and aligned to 32-pixel
boundaries of the raw frame. With 10-bit Bayer stored in 16-bit containers,
that is 64 bytes, i.e. one CPU cache line.
- The artifacts appear with libcamera's software ISP in both GPU mode and CPU
mode (LIBCAMERA_SOFTISP_MODE=cpu), so they are already present in the raw
buffer delivered by intel-ipu7-isys.
- This matches the patch "media: staging/ipu7: Synchronize capture buffers at
the vb2 boundaries" (LKML, August 2026). It explains that
dma_sync_sgtable_for_{cpu,device}() perform no cache maintenance on x86, so
stale cached frame data from an earlier buffer slot survives buffer handoff.
The patch calls ipu7_dma_sync_sgtable() from buf_prepare and buf_finish.
https://ratatoskr.run/lkml/2026/08/17455941
Steps to reproduce:
1. Open GNOME Snapshot (or `cam -c1 --capture` / any libcamera client).
2. Move a hand quickly in front of the camera and take a photo.
3. Observe colored 32-pixel horizontal dashes along moving edges.
Expected: clean frames without mixed-in data from earlier frames.
Versions:
- Ubuntu 26.10, kernel 7.3.0-9-generic (also not fixed in the 7.3.0-10.10
changelog)
- libcamera 0.7.0-1ubuntu2 (simple pipeline handler, software ISP)
- Machine: ThinkPad X9-15 Gen 1 (21Q60068BM), BIOS N4CET46W (1.22)
Request: please consider backporting the above patch (or the merged
upstream equivalent) to the Ubuntu kernel's staging ipu7 driver.
ProblemType: Bug
DistroRelease: Ubuntu 26.10
Package: linux-image-7.3.0-9-generic 7.3.0-9.9
ProcVersionSignature: Ubuntu 7.3.0-9.9-generic 7.3.0-rc6
Uname: Linux 7.3.0-9-generic x86_64
ApportVersion: 2.36.0-0ubuntu1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: milen 3926 F.... pipewire
milen 20413 F.... wireplumber
/dev/snd/seq: milen 3926 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Oct 30 00:20:23 2026
InstallationDate: Installed on 2026-10-26 (3 days ago)
InstallationMedia: Ubuntu 26.04.1 LTS "Resolute Raccoon" - Release amd64
(20260826)
MachineType: LENOVO 21Q60068BM
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 xedrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.3.0-9-generic
root=UUID=4a259af1-cc51-483b-bfd7-f0aec4937876 ro quiet splash
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
SourcePackage: linux
StagingDrivers: intel_ipu7_isys intel_ipu7
UpgradeStatus: Upgraded to stonking on 2026-10-28 (1 days ago)
dmi.bios.date: 08/14/2026
dmi.bios.release: 1.22
dmi.bios.vendor: LENOVO
dmi.bios.version: N4CET46W (1.22 )
dmi.board.asset.tag: Not Available
dmi.board.name: 21Q60068BM
dmi.board.vendor: LENOVO
dmi.board.version: SDK0T76576 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.ec.firmware.release: 1.15
dmi.modalias:
dmi:bvnLENOVO:bvrN4CET46W(1.22):bd08/14/2026:br1.22:efr1.15:svnLENOVO:pn21Q60068BM:pvrThinkPadX9-15Gen1:rvnLENOVO:rn21Q60068BM:rvrSDK0T76576WIN:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_21Q6_BU_Think_FM_ThinkPadX9-15Gen1:pfaThinkPadX9-15Gen1:
dmi.product.family: ThinkPad X9-15 Gen 1
dmi.product.name: 21Q60068BM
dmi.product.sku: LENOVO_MT_21Q6_BU_Think_FM_ThinkPad X9-15 Gen 1
dmi.product.version: ThinkPad X9-15 Gen 1
dmi.sys.vendor: LENOVO
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug staging stonking third-party-packages wayland-session
** Attachment added: "ipu7-launchpad-bug.md"
https://bugs.launchpad.net/bugs/2172563/+attachment/6013556/+files/ipu7-launchpad-bug.md
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https://bugs.launchpad.net/bugs/2172563
Title:
[IPU7] Stale 64-byte cache lines in captured frames (colored
horizontal dashes on motion) - please backport "media: staging/ipu7:
Synchronize capture buffers at the vb2 boundaries"
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