[PATCH] cpufreq: intel_pstate: Fix active mode offline/online EPP handling

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

After commit 4adcf2e5829f ("cpufreq: intel_pstate: Add ->offline and
->online callbacks") the EPP value set by the "performance" scaling
algorithm in the active mode is not restored after an offline/online
cycle which replaces it with the saved EPP value coming from user
space.

Address this issue by forcing intel_pstate_hwp_set() to set a new
EPP value when it runs first time after online.

Fixes: 4adcf2e5829f ("cpufreq: intel_pstate: Add ->offline and ->online callbacks")
Link: https://lore.kernel.org/linux-pm/adc7132c8655bd4d1c8b6129578e931a14fe1db2.camel@linux.intel.com/
Reported-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: 5.9+ <stable@vger.kernel.org> # 5.9+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpufreq/intel_pstate.c |    6 ++++++
 1 file changed, 6 insertions(+)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -1006,6 +1006,12 @@ static void intel_pstate_hwp_offline(str
 		 */
 		value &= ~GENMASK_ULL(31, 24);
 		value |= HWP_ENERGY_PERF_PREFERENCE(cpu->epp_cached);
+		/*
+		 * However, make sure that EPP will be set to "performance" when
+		 * the CPU is brought back online again and the "performance"
+		 * scaling algorithm is still in effect.
+		 */
+		cpu->epp_policy = CPUFREQ_POLICY_UNKNOWN;
 	}
 
 	/*