[PATCH 0/1][SRU][N][O][Unstable] Random flickering with Intel i915 (Comet Lake and Kaby Lake) on Linux 6.8+

[AceLan Kao]

From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/2086587

[Impact]
The flickering predominantly occurs when the mouse cursor is in the bottom
quarter of the screen and stops when the cursor leaves this area.
Extensive testing across various kernel versions revealed that the issue
became apparent from kernel version 6.8.0 onward, correlating with the
mentioned configuration changes, CONFIG_INTEL_IOMMU_DEFAULT_ON and
CONFIG_INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON.
The problem persists in the latest drm tip.

[Fix]
As an immediate workaround, adding 'intel_iommu=igfx_off' to the kernel
command line has been found to effectively eliminate the flickering issue.
This patch proposes the same behavior as 'intel_iommu=igfx_off' and apply
the rule to all Intel KBL and CML GPU IDs.

[Test]
1. Boot up to desktop with ubuntu kernels(6.8+)
2. Moving cursor around the desktop
3. There should be no flicker while cursor is moving

[Where problems could occur]
For virtualized environments using hardware-assisted virtualization for
graphics (such as VFIO or mediated pass-through), disabling IOMMU for
graphics could either disable these features or reduce their security and
efficiency.
Usually, users pass the 'intel_iommu=on' by themselves when they are
using related features. So, the impact of this change is minimal.

Chia-Lin Kao (AceLan) (1):
  UBUNTU: SAUCE: iommu/intel: disable DMAR for KBL and CML integrated
    gfx

 drivers/iommu/intel/iommu.c | 41 +++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

-- 
2.43.0