Linux Will Finally Stop Flickering With AMD Stoney Ridge On 4K Displays
Written by Michael Larabel in AMD on 20 February 2020 at 02:19 AM EST. 15 Comments
AMD --
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.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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