x86/aperfmperf: Integrate the fallback code from show_cpuinfo()

Due to the avoidance of IPIs to idle CPUs arch_freq_get_on_cpu() can return
0 when the last sample was too long ago.

show_cpuinfo() has a fallback to cpufreq_quick_get() and if that fails to
return cpu_khz, but the readout code for the per CPU scaling frequency in
sysfs does not.

Move that fallback into arch_freq_get_on_cpu() so the behaviour is the same
when reading /proc/cpuinfo and /sys/..../cur_scaling_freq.
Suggested-by: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Doug Smythies <dsmythies@telus.net>
Link: https://lore.kernel.org/r/87pml5180p.ffs@tglx

arch/x86/kernel/cpu/aperfmperf.c

@@ -405,12 +405,12 @@ void arch_scale_freq_tick(void)
 unsigned int arch_freq_get_on_cpu(int cpu)
 {
 	struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
+	unsigned int seq, freq;
 	unsigned long last;
-	unsigned int seq;
 	u64 acnt, mcnt;
 
 	if (!cpu_feature_enabled(X86_FEATURE_APERFMPERF))
-		return 0;
+		goto fallback;
 
 	do {
 		seq = raw_read_seqcount_begin(&s->seq);
@@ -424,9 +424,13 @@ unsigned int arch_freq_get_on_cpu(int cpu)
 	 * which covers idle and NOHZ full CPUs.
 	 */
 	if (!mcnt || (jiffies - last) > MAX_SAMPLE_AGE)
-		return 0;
+		goto fallback;
 
 	return div64_u64((cpu_khz * acnt), mcnt);
+
+fallback:
+	freq = cpufreq_quick_get(cpu);
+	return freq ? freq : cpu_khz;
 }
 
 static int __init bp_init_aperfmperf(void)

arch/x86/kernel/cpu/proc.c

@@ -86,12 +86,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 	if (cpu_has(c, X86_FEATURE_TSC)) {
 		unsigned int freq = arch_freq_get_on_cpu(cpu);
 
-		if (!freq)
-			freq = cpufreq_quick_get(cpu);
-		if (!freq)
-			freq = cpu_khz;
-		seq_printf(m, "cpu MHz\t\t: %u.%03u\n",
-			   freq / 1000, (freq % 1000));
+		seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
 	}
 
 	/* Cache size */