Freedreno's MSM DRM Driver Wires In DEVFREQ Re-Clocking Support

Freedreno open-source Qualcomm Adreno driver creator Rob Clark has sent in the set of updates for the MSM DRM driver targeting the Linux 4.16 kernel.

The MSM Direct Rendering Manager updates for DRM-Next to go into Linux 4.16 are a bit late for the DRM staging, but these changes are mostly small. Besides some bug fixes and other minor code changes, the main feature addition for MSM in Linux 4.16 is DEVFREQ support for controlling the GPU clock frequency.

DEVFREQ (or stylized as "devfreq") is the generic dynamic voltage and frequency scaling (DVFS) framework for non-CPU devices. DEVFREQ was originally developed by Samsung but is generic enough for any other drivers to also make use of it for frequency and voltage control. With Linux 4.16, MSM is using DEVFREQ for dynamically controlling the GPU frequency using its "simple_ondemand" governor for adjusting the frequencies based upon load.

This DEVFREQ support came courtesy of Qualcomm via their CodeAurora initiative. CodeAurora developers continue contributing to this open-source Freedreno/MSM driver stack that started out via reverse-engineering.

The MSM changes for Linux 4.16 can be found via this pull request.