[Bug 194966] New: Radeon KMS driver lack power and clocks management support

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194966

            Bug ID: 194966
           Summary: Radeon KMS driver lack power and clocks management
                    support
           Product: Base System
           Version: 10.1-RC2
          Hardware: Any
                OS: Any
            Status: Needs Triage
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: zuborg at gmail.com

Created attachment 149319
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=149319&action=edit
Patch /sys/dev/drm2/. radeonkms driver change device sclk and mclk when
initializing according to drm.force_sclk and drm.force_mclk loader.conf
tuneables

Radeon KMS driver initialize hardware in default 'performance' mode, which
cause significant noise and power consumption.

Following patch adds rudimentary support of engine/memory clocks management.

Immediately after initialization driver looks at value of drm.force_sclk and
drm.force_mclk variables (tuneable via loader.conf). If non-zero value
specified driver call radeon_set_engine_clock()/radeon_set_memory_clock() to
adjust clocks setting.

Boundary checks are not performed, it should be used with care!

Actually it would be significantly better to add direct support of
clocks/voltage values by `sysctl` on the fly, not only via loader.conf as in
proposed patch.

Patch was tested, values (in MHz)
  drm.force_sclk=250
  drm.force_mclk=250
reduce noise of card fan very noticeable.

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