[Bug 209202] [PATCH] [powermac_thermal] In-Kernel PowerMac fan control does not effectively regular some quad core models

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=209202

            Bug ID: 209202
           Summary: [PATCH] [powermac_thermal] In-Kernel PowerMac fan
                    control does not effectively regular some quad core
                    models
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: ppc
                OS: Any
            Status: New
          Keywords: patch
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: gmbroome at vcu.edu
          Keywords: patch

Created attachment 169882
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=169882&action=edit
Patch to add additional temp level and longer hysteresis to PowerMac thermal
management

The in-kernel fan control for PowerMac systems works reasonably well for
single- and dual-core systems, but has mixed results for quad-core systems
based on the system condition and CPU assembly revision.

For "revision 1" CPU assemblies (one shared radiator and pump) in quad-core
PowerMac G5 units, the system runs extremely hot, hitting critical temperature
and forcibly shutting down during even moderate CPU utilization.

For "revision 2" CPU assemblies (a discrete radiator and pump for each CPU
package), the fans run at high baseline levels, though the system does not
typically reach critical temperature or forcibly shut down.

The attached patch, which includes changes to powermac_thermal.[c|h], smu.c,
and smusat.c, adds an intermediate temperature target above which fans and
pumps run at full speed, but which is still well below the critical temperature
that forces a shutdown.

In testing, this leaves the "revision 1" quad-core systems usable, albeit
noisy.  Quad-core systems using the "revision 2" CPU assembly scale fan and
pump speed more aggressively, but run them at lower levels during idling.  The
dual-core system tested remained largely unaffected by the changes.  The patch
is not expected to affect anything but the last generation of PowerMac models,
i.e. only ones with an SMU.

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