[PATCH v1] cpufreq: intel_pstate: Avoid using DESIRED_PERF when DEC is enabled

["Rafael J. Wysocki" <rafael@kernel.org>]

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

In principle, the desired performance level can be set in MSR_HWP_REQUEST
to indicate to the processor what performance level the OS would like
the given CPU to run at, but if the Dynamic Efficiency Control (DEC)
feature is enabled in the processor, doing so may result in confusing
the processor firmware.  It is then better to let the processor firmware
figure out the most suitable performance level by itself.

Accordingly, make intel_pstate always set the desired performance level
to zero (which means "no preference") when running on a platform with
DEC enabled.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

Applies on top of linux-next.

---
 drivers/cpufreq/intel_pstate.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -303,6 +303,7 @@ static bool per_cpu_limits __ro_after_in
 static bool hwp_forced __ro_after_init;
 static bool hwp_boost __read_mostly;
 static bool hwp_is_hybrid;
+static u32 hwp_desired_mask __read_mostly = ~0U;
 
 static struct cpufreq_driver *intel_pstate_driver __read_mostly;
 
@@ -3150,7 +3151,7 @@ static void intel_cpufreq_hwp_update(str
 	value |= HWP_MAX_PERF(max);
 
 	value &= ~HWP_DESIRED_PERF(~0L);
-	value |= HWP_DESIRED_PERF(desired);
+	value |= HWP_DESIRED_PERF(desired & hwp_desired_mask);
 
 	if (value == prev)
 		return;
@@ -3787,6 +3788,7 @@ static int __init intel_pstate_init(void
 	id = x86_match_cpu(hwp_support_ids);
 	if (id) {
 		bool epp_present = hwp_check_epp();
+		bool dec_present = hwp_check_dec();
 
 		/*
 		 * If HWP is enabled already, there is no choice but to deal
@@ -3798,7 +3800,7 @@ static int __init intel_pstate_init(void
 			no_hwp = 0;
 		} else if (no_load) {
 			return -ENODEV;
-		} else if (!epp_present && !hwp_check_dec()) {
+		} else if (!epp_present && !dec_present) {
 			/*
 			 * Avoid enabling HWP for processors without EPP support
 			 * unless the Dynamic Efficiency Control (DEC) enable
@@ -3820,6 +3822,9 @@ static int __init intel_pstate_init(void
 			if (!default_driver)
 				default_driver = &intel_pstate;
 
+			if (dec_present)
+				hwp_desired_mask = 0;
+
 			if (!id->driver_data)
 				pstate_funcs.get_cpu_scaling = hwp_get_cpu_scaling;