AMD Finally Enabling PSR By Default For Newer Hardware With Linux 5.16

With it getting late into the Linux 5.15 kernel cycle, the focus is shifting by the Direct Rendering Driver maintainers from new feature work targeting the next cycle (5.16) to instead on bug fixes. AMD sent out a pull request of new AMDGPU Linux 5.16 material this week that is primarily delivering bug fixes but one notable addition is finally enabling PSR by default for newer GPUs.

In prior weeks the AMDGPU pull requests to DRM-Next for Linux 5.16 have brought initial DisplayPort 2.0 enablement, Cyan Skillfish display support, USB4 DisplayPort tunneling, and other changes.

This week's pull request to DRM-Next for the 5.16 merge window now includes more fixes around the Cyan Skillfish Navi 1x APU support, IP discovery enumeration fixes, display fixes, RAS fixes for Aldebaran, IOMMU fixes for Raven Ridge, and other fixes.

One patch tucked away within this pull request that brings some excitement is enabling PSR by default on newer DCN hardware. Yes, Panel Self Refresh finally being enabled by default for newer hardware. Though at this time that newer hardware seeing the support is for Yellow Carp (Rembrandt) with DCN 3.1. GPUs with pre-DCN-3.1 hardware are keeping PSR off for now. Panel Self Refresh os a power-savings feature for when the display/monitor contents is static by being able to power-down extra circuitry.

While PSR is an industry standard, it's proven to be quirky too for Intel hardware and various laptop display panels out there so they've also seen challenges on the other side of the table. AMD left their PSR support disabled to now due to issues with some desktop compositors not page-flipping and scanning out correctly in a manner that worked with their PSR handling. AMD now better handles the compositors out there and so feels it's safe to enable Panel Self Refresh by default. But due to the possibility of bugs/regressions, at least for now AMD isn't enabling PSR for existing hardware and thus just setting it by default for DCN 3.1 and newer display hardware. We'll see after a while if they decide to flip on PSR for existing AMD hardware.

The list of patches for this latest AMDGPU/AMDKFD pull request to DRM-Next can be found here.