drm/i915: add dynamic clock frequency control
There are several sources of unnecessary power consumption on Intel graphics systems. The first is the LVDS clock. TFTs don't suffer from persistence issues like CRTs, and so we can reduce the LVDS refresh rate when the screen is idle. It will be automatically upclocked when userspace triggers graphical activity. Beyond that, we can enable memory self refresh. This allows the memory to go into a lower power state when the graphics are idle. Finally, we can drop some clocks on the gpu itself. All of these things can be reenabled between frames when GPU activity is triggered, and so there should be no user visible graphical changes. Signed-off-by: Jesse Barnes <jesse.barnes@intel.com> Signed-off-by: Matthew Garrett <mjg@redhat.com> Signed-off-by: Eric Anholt <eric@anholt.net>
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