cpufreq: powernow-k6: Fix double invocation of cpufreq_freq_transition_begin/end

During frequency transitions, the cpufreq core takes the responsibility of
invoking cpufreq_freq_transition_begin() and cpufreq_freq_transition_end()
for those cpufreq drivers that define the ->target_index callback but don't
set the ASYNC_NOTIFICATION flag.

The powernow-k6 cpufreq driver falls under this category, but this driver was
invoking the _begin() and _end() APIs itself around frequency transitions,
which led to double invocation of the _begin() API. The _begin API makes
contending callers wait until the previous invocation is complete. Hence,
the powernow-k6 driver ended up waiting on itself, leading to system hangs
during boot.

Fix this by removing the calls to the _begin() and _end() APIs from the
powernow-k6 driver, since they rightly belong to the cpufreq core.

(Note that during ->exit(), the powernow-k6 driver sets the frequency
 without any help from the cpufreq core. So add explicit calls to the
 _begin() and _end() APIs around that frequency transition alone, to take
 care of that special case. Also, add a missing 'break' statement there.)

Fixes: 12478cf0c55e (cpufreq: Make sure frequency transitions are serialized)
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/powernow-k6.c

@@ -138,22 +138,14 @@ static void powernow_k6_set_cpu_multiplier(unsigned int best_i)
 static int powernow_k6_target(struct cpufreq_policy *policy,
 		unsigned int best_i)
 {
-	struct cpufreq_freqs freqs;
 
 	if (clock_ratio[best_i].driver_data > max_multiplier) {
 		printk(KERN_ERR PFX "invalid target frequency\n");
 		return -EINVAL;
 	}
 
-	freqs.old = busfreq * powernow_k6_get_cpu_multiplier();
-	freqs.new = busfreq * clock_ratio[best_i].driver_data;
-
-	cpufreq_freq_transition_begin(policy, &freqs);
-
 	powernow_k6_set_cpu_multiplier(best_i);
 
-	cpufreq_freq_transition_end(policy, &freqs, 0);
-
 	return 0;
 }
 
@@ -229,8 +221,18 @@ static int powernow_k6_cpu_exit(struct cpufreq_policy *policy)
 	unsigned int i;
 
 	for (i = 0; (clock_ratio[i].frequency != CPUFREQ_TABLE_END); i++) {
-		if (clock_ratio[i].driver_data == max_multiplier)
+		if (clock_ratio[i].driver_data == max_multiplier) {
+			struct cpufreq_freqs freqs;
+
+			freqs.old = policy->cur;
+			freqs.new = clock_ratio[i].frequency;
+			freqs.flags = 0;
+
+			cpufreq_freq_transition_begin(policy, &freqs);
 			powernow_k6_target(policy, i);
+			cpufreq_freq_transition_end(policy, &freqs, 0);
+			break;
+		}
 	}
 	return 0;
 }