[PATCH v3] Documentation/cpu-freq: add intel-pstate.txt

[Ramkumar Ramachandra]

The Intel P-state driver is currently undocumented. Add some
documentation based on the cover-letter sent with the original series.

Cc: Dirk Brandewie <dirk.brandewie@xxxxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Linux PM <linux-pm@xxxxxxxxxxxxxxx>
Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Signed-off-by: Ramkumar Ramachandra <artagnon@xxxxxxxxx>
---
 Documentation/cpu-freq/intel-pstate.txt | 40 +++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 Documentation/cpu-freq/intel-pstate.txt

diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
new file mode 100644
index 0000000..e742d21
--- /dev/null
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -0,0 +1,40 @@
+Intel P-state driver
+--------------------
+
+This driver implements a scaling driver with an internal governor for
+Intel Core processors.  The driver follows the same model as the
+Transmeta scaling driver (longrun.c) and implements the setpolicy()
+instead of target().  Scaling drivers that implement setpolicy() are
+assumed to implement internal governors by the cpufreq core. All the
+logic for selecting the current P state is contained within the
+driver; no external governor is used by the cpufreq core.
+
+Intel SandyBridge+ processors are supported.
+
+New sysfs files for controlling P state selection have been added to
+/sys/devices/system/cpu/intel_pstate/
+
+      max_perf_pct: limits the maximum P state that will be requested by
+      the driver stated as a percentage of the available performance.
+
+      min_perf_pct: limits the minimum P state that will be  requested by
+      the driver stated as a percentage of the available performance.
+
+      no_turbo: limits the driver to selecting P states below the turbo
+      frequency range.
+
+For contemporary Intel processors, the frequency is controlled by the
+processor itself and the P-states exposed to software are related to
+performance levels.  The idea that frequency can be set to a single
+frequency is fiction for Intel Core processors. Even if the scaling
+driver selects a single P state the actual frequency the processor
+will run at is selected by the processor itself.
+
+New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
+
+      deadband
+      d_gain_pct
+      i_gain_pct
+      p_gain_pct
+      sample_rate_ms
+      setpoint
-- 
1.8.5.2.227.g53f3478

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