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

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: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
Reviewed-by: Zeng Heng <zengheng4@huawei.com>
Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 1a5ad184d28fc24e318f17e4cdad06efbb74ad90..646b466002c6a2004e415379a7a43ea82d42275f 100644 (file)
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/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;
@@ -724,13 +727,31 @@ 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};
@@ -746,18 +767,32 @@ 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);
 }