From: "Rafael J. Wysocki" <rafael.j.wyso...@intel.com>
Modify the EPP sysfs interface to reject attempts to change the EPP
to values different from 0 ("performance") in the active mode with
the "performance" policy (ie. scaling_governor set to "performance"),
to avoid situations in which the kernel appears to discard data
passed to it via the EPP sysfs attribute.
Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
Reviewed-by: Artem Bityutskiy <artem.bityuts...@linux.intel.com>
---
v2 -> v3: New patch
v3 -> v4: Add the R-by from Artem
---
Documentation/admin-guide/pm/intel_pstate.rst | 4 +++-
drivers/cpufreq/intel_pstate.c | 8 ++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/pm/intel_pstate.rst
b/Documentation/admin-guide/pm/intel_pstate.rst
index cdd1a9a7f9a2..5072e7064d13 100644
--- a/Documentation/admin-guide/pm/intel_pstate.rst
+++ b/Documentation/admin-guide/pm/intel_pstate.rst
@@ -123,7 +123,9 @@ Energy-Performance Bias (EPB) knob (otherwise), which means
that the processor's
internal P-state selection logic is expected to focus entirely on performance.
This will override the EPP/EPB setting coming from the ``sysfs`` interface
-(see `Energy vs Performance Hints`_ below).
+(see `Energy vs Performance Hints`_ below). Moreover, any attempts to change
+the EPP/EPB to a value different from 0 ("performance") via ``sysfs`` in this
+configuration will be rejected.
Also, in this configuration the range of P-states available to the processor's
internal P-state selection logic is always restricted to the upper boundary
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index e540448e0bd0..b308c39b6204 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -684,6 +684,14 @@ static int intel_pstate_set_energy_pref_index(struct
cpudata *cpu_data,
else if (epp == -EINVAL)
epp = epp_values[pref_index - 1];
+ /*
+ * To avoid confusion, refuse to set EPP to any values different
+ * from 0 (performance) if the current policy is "performance",
+ * because those values would be overridden.
+ */
+ if (epp > 0 && cpu_data->policy == CPUFREQ_POLICY_PERFORMANCE)
+ return -EBUSY;
+
ret = intel_pstate_set_epp(cpu_data, epp);
} else {
if (epp == -EINVAL)
--
2.26.2
