cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged

BugLink: https://bugs.launchpad.net/bugs/2086233

The CPPC performance feedback counters could be 0 or unchanged when the
target cpu is in a low-power idle state, e.g. power-gated or clock-gated.

When the counters are 0, cppc_cpufreq_get_rate() returns 0 KHz, which makes
cpufreq_online() get a false error and fail to generate a cpufreq policy.

When the counters are unchanged, the existing cppc_perf_from_fbctrs()
returns a cached desired perf, but some platforms may update the real
frequency back to the desired perf reg.

For the above cases in cppc_cpufreq_get_rate(), get the latest desired perf
from the CPPC reg to reflect the frequency because some platforms may
update the actual frequency back there; if failed, use the cached desired
perf.

Fixes: 6a4fec4 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
Signed-off-by: Jie Zhan <[email protected]>
Reviewed-by: Zeng Heng <[email protected]>
Reviewed-by: Ionela Voinescu <[email protected]>
Reviewed-by: Huisong Li <[email protected]>
Signed-off-by: Viresh Kumar <[email protected]>
(cherry picked from commit c471956 linux-next)
Signed-off-by: Jamie Nguyen <[email protected]>
Tested-by: Carol Soto <[email protected]>
Acked-by: Brad Figg <[email protected]>
Acked-by: Carol L Soto <[email protected]>
Acked-by: Koba Ko <[email protected]>
Signed-off-by: Brad Figg <[email protected]>
Acked-by: Noah Wager <[email protected]>
Acked-by: Jacob Martin <[email protected]>

drivers/cpufreq/cppc_cpufreq.c

@@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work)
 
 	perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs,
 				     &fb_ctrs);
+	if (!perf)
+		return;
+
 	cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
 
 	perf <<= SCHED_CAPACITY_SHIFT;
@@ -730,13 +733,31 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
 	delta_delivered = get_delta(fb_ctrs_t1->delivered,
 				    fb_ctrs_t0->delivered);
 
-	/* Check to avoid divide-by zero and invalid delivered_perf */
+	/*
+	 * Avoid divide-by zero and unchanged feedback counters.
+	 * Leave it for callers to handle.
+	 */
 	if (!delta_reference || !delta_delivered)
-		return cpu_data->perf_ctrls.desired_perf;
+		return 0;
 
 	return (reference_perf * delta_delivered) / delta_reference;
 }
 
+static int cppc_get_perf_ctrs_sample(int cpu,
+				     struct cppc_perf_fb_ctrs *fb_ctrs_t0,
+				     struct cppc_perf_fb_ctrs *fb_ctrs_t1)
+{
+	int ret;
+
+	ret = cppc_get_perf_ctrs(cpu, fb_ctrs_t0);
+	if (ret)
+		return ret;
+
+	udelay(2); /* 2usec delay between sampling */
+
+	return cppc_get_perf_ctrs(cpu, fb_ctrs_t1);
+}
+
 static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 {
 	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
@@ -752,18 +773,32 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 
 	cpufreq_cpu_put(policy);
 
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
-	if (ret)
-		return 0;
-
-	udelay(2); /* 2usec delay between sampling */
-
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
-	if (ret)
-		return 0;
+	ret = cppc_get_perf_ctrs_sample(cpu, &fb_ctrs_t0, &fb_ctrs_t1);
+	if (ret) {
+		if (ret == -EFAULT)
+			/* Any of the associated CPPC regs is 0. */
+			goto out_invalid_counters;
+		else
+			return 0;
+	}
 
 	delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
 					       &fb_ctrs_t1);
+	if (!delivered_perf)
+		goto out_invalid_counters;
+
+	return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
+
+out_invalid_counters:
+	/*
+	 * Feedback counters could be unchanged or 0 when a cpu enters a
+	 * low-power idle state, e.g. clock-gated or power-gated.
+	 * Use desired perf for reflecting frequency.  Get the latest register
+	 * value first as some platforms may update the actual delivered perf
+	 * there; if failed, resort to the cached desired perf.
+	 */
+	if (cppc_get_desired_perf(cpu, &delivered_perf))
+		delivered_perf = cpu_data->perf_ctrls.desired_perf;
 
 	return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
 }