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. 28 Comments
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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