AMDGPU To Allow Memory Re-Clocking Soon For Multi-Monitor Setups
Written by Michael Larabel in Radeon on 23 August 2019 at 03:04 AM EDT. 22 Comments
RADEON --
Currently the AMDGPU Linux kernel driver doesn't automatically adjust the video memory clock speeds when running a multi-monitor setup since it's more complicated to gracefully handle when scanning out to two or more displays. But a set of currently experimental patches will allow memory clock switching support on multi-monitor setups with the AMDGPU DC code.

Alex Deucher of AMD sent out the kernel driver patches today for allowing memory clock switching/re-clocking support for multi-monitor setups so long as the displays are synchronized. Alex explained with the four patches, "This patch set enables mclk switching with multiple monitors when all
monitors are sync. Normally mclk switching is not available with multiple monitors because the vblank timing does not line up. However, if the timing is identical, the display driver can sync up the displays in some cases.
"

Right now the video memory clocks are stuck to their highest speeds when in a multi-monitor configuration while these patches will allow for down-clocking when possible to save power, similar to the behavior on single-head setups when not having to worry about cross-monitor synchronization.

Initially at least this new functionality will be disabled by default but can be enabled for interested users with the amdgpu.dcfeaturemask=2 kernel parameter once this support lands into potentially Linux 5.4 or later.
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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 10,000 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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