[Bug 2086587] Re: Random flickering with Intel i915 (Comet Lake and Kaby Lake) on Linux 6.8

Thank you for this test kernel and patch.

I'll use and test it for some days and let you know the results.

$ lspci -nnk | grep -A3 VGA
00:02.0 VGA compatible controller [0300]: Intel Corporation HD Graphics 630 [8086:591b] (rev 04)
DeviceName: Onboard IGD
Subsystem: ASUSTeK Computer Inc. HD Graphics 630 [1043:15e0]
Kernel driver in use: i915

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

Title:
Random flickering with Intel i915 (Comet Lake and Kaby Lake) on Linux
6.8

Status in linux package in Ubuntu:
In Progress
Status in linux source package in Jammy:
Invalid
Status in linux source package in Noble:
In Progress
Status in linux source package in Oracular:
In Progress
Status in linux source package in Plucky:
In Progress

Bug description:
[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 SKL GPU IDs.

[Test]
1. Boot up to desktop with 6.8.0-x kernels
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.

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