Linux Will Finally Stop Flickering With AMD Stoney Ridge On 4K Displays

For those still running the AMD "Stoney Ridge" mobile APUs from 2016 that were launched aside Bristol Ridge with Excavator-based CPU cores and GCN 1.2 graphics, the Linux kernel has a fix finally for flickering issues when driving a 4K display off the APU.

It turns out the fix for this 4K flickering issue on Stoney Ridge APUs is to disable IOMMU support for the hardware. Canonical's Kai-Heng Feng explained in the patch, "Serious screen flickering when Stoney Ridge outputs to a 4K monitor. Use identity-mapping and PCI ATS doesn't help this issue. According to Alex Deucher, IOMMU isn't enabled on Windows, so let's do the same here to avoid screen flickering on 4K monitor."

Going back to at least last year has been bug reports about screen flickering when running at 4K with Stoney Ridge hardware. Back then it was also noted when booting the kernel with iommu=off, screen flickering didn't occur.

The change is blanket disabling IOMMU for systems with Stoney Ridge graphics. It looks to be a case of Stoney Ridge's IOMMU capabilities being stoned.