Merge tag 'pm-6.12-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull power management fixes from Rafael Wysocki:
 "Update cpufreq documentation to match the code after recent changes
  (Christian Loehle), fix a units conversion issue in the CPPC cpufreq
  driver (liwei), and fix an error check in the dtpm_devfreq power
  capping driver (Yuan Can)"

* tag 'pm-6.12-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  cpufreq: CPPC: fix perf_to_khz/khz_to_perf conversion exception
  powercap: dtpm_devfreq: Fix error check against dev_pm_qos_add_request()
  cpufreq: docs: Reflect latency changes in docs

Author: torvalds

Documentation/admin-guide/pm/cpufreq.rst

@@ -425,8 +425,8 @@ This governor exposes only one tunable:
 
 ``rate_limit_us``
 	Minimum time (in microseconds) that has to pass between two consecutive
-	runs of governor computations (default: 1000 times the scaling driver's
-	transition latency).
+	runs of governor computations (default: 1.5 times the scaling driver's
+	transition latency or the maximum 2ms).
 
 	The purpose of this tunable is to reduce the scheduler context overhead
 	of the governor which might be excessive without it.
@@ -474,17 +474,17 @@ This governor exposes the following tunables:
 	This is how often the governor's worker routine should run, in
 	microseconds.
 
-	Typically, it is set to values of the order of 10000 (10 ms).  Its
-	default value is equal to the value of ``cpuinfo_transition_latency``
-	for each policy this governor is attached to (but since the unit here
-	is greater by 1000, this means that the time represented by
-	``sampling_rate`` is 1000 times greater than the transition latency by
-	default).
+	Typically, it is set to values of the order of 2000 (2 ms).  Its
+	default value is to add a 50% breathing room
+	to ``cpuinfo_transition_latency`` on each policy this governor is
+	attached to. The minimum is typically the length of two scheduler
+	ticks.
 
 	If this tunable is per-policy, the following shell command sets the time
-	represented by it to be 750 times as high as the transition latency::
+	represented by it to be 1.5 times as high as the transition latency
+	(the default)::
 
-	# echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate
+	# echo `$(($(cat cpuinfo_transition_latency) * 3 / 2)) > ondemand/sampling_rate
 
 ``up_threshold``
 	If the estimated CPU load is above this value (in percent), the governor

drivers/acpi/cppc_acpi.c

@@ -1916,9 +1916,15 @@ unsigned int cppc_perf_to_khz(struct cppc_perf_caps *caps, unsigned int perf)
 	u64 mul, div;
 
 	if (caps->lowest_freq && caps->nominal_freq) {
-		mul = caps->nominal_freq - caps->lowest_freq;
+		/* Avoid special case when nominal_freq is equal to lowest_freq */
+		if (caps->lowest_freq == caps->nominal_freq) {
+			mul = caps->nominal_freq;
+			div = caps->nominal_perf;
+		} else {
+			mul = caps->nominal_freq - caps->lowest_freq;
+			div = caps->nominal_perf - caps->lowest_perf;
+		}
 		mul *= KHZ_PER_MHZ;
-		div = caps->nominal_perf - caps->lowest_perf;
 		offset = caps->nominal_freq * KHZ_PER_MHZ -
 			 div64_u64(caps->nominal_perf * mul, div);
 	} else {
@@ -1939,11 +1945,17 @@ unsigned int cppc_khz_to_perf(struct cppc_perf_caps *caps, unsigned int freq)
 {
 	s64 retval, offset = 0;
 	static u64 max_khz;
-	u64  mul, div;
+	u64 mul, div;
 
 	if (caps->lowest_freq && caps->nominal_freq) {
-		mul = caps->nominal_perf - caps->lowest_perf;
-		div = caps->nominal_freq - caps->lowest_freq;
+		/* Avoid special case when nominal_freq is equal to lowest_freq */
+		if (caps->lowest_freq == caps->nominal_freq) {
+			mul = caps->nominal_perf;
+			div = caps->nominal_freq;
+		} else {
+			mul = caps->nominal_perf - caps->lowest_perf;
+			div = caps->nominal_freq - caps->lowest_freq;
+		}
 		/*
 		 * We don't need to convert to kHz for computing offset and can
 		 * directly use nominal_freq and lowest_freq as the div64_u64

drivers/powercap/dtpm_devfreq.c

@@ -178,7 +178,7 @@ static int __dtpm_devfreq_setup(struct devfreq *devfreq, struct dtpm *parent)
 	ret = dev_pm_qos_add_request(dev, &dtpm_devfreq->qos_req,
 				     DEV_PM_QOS_MAX_FREQUENCY,
 				     PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
-	if (ret) {
+	if (ret < 0) {
 		pr_err("Failed to add QoS request: %d\n", ret);
 		goto out_dtpm_unregister;
 	}