[PATCH 2/2] cpufreq: powernv: Use PMSR to verify global and local pstate

[Akshay Adiga]

As fast_switch may get called in interrupt disable mode, it does not
update the global_pstate_info data structure. Hence the global_pstate_info
has stale data whenever pstate is updated through fast_swtich().

So the gpstate_timer can fire after a fast_switch() call has update
the pstates to a different value. Hence the timer handler cannot rely
on the cached values of local and global pstate and needs to read it
from the PMSR. 

Signed-off-by: Akshay Adiga <akshay.ad...@linux.vnet.ibm.com>

---
 drivers/cpufreq/powernv-cpufreq.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c 
b/drivers/cpufreq/powernv-cpufreq.c
index 09a0496..57713b5 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -592,7 +592,8 @@ void gpstate_timer_handler(unsigned long data)
 {
        struct cpufreq_policy *policy = (struct cpufreq_policy *)data;
        struct global_pstate_info *gpstates = policy->driver_data;
-       int gpstate_idx;
+       int gpstate_idx, lpstate_idx;
+       unsigned long val;
        unsigned int time_diff = jiffies_to_msecs(jiffies)
                                        - gpstates->last_sampled_time;
        struct powernv_smp_call_data freq_data;
@@ -600,21 +601,36 @@ void gpstate_timer_handler(unsigned long data)
        if (!spin_trylock(&gpstates->gpstate_lock))
                return;
 
+       /*
+        * If PMCR was last updated was using fast_swtich then
+        * We may have wrong in gpstate->last_lpstate_idx
+        * value. Hence, read from PMCR to get correct data.
+        */
+       val = get_pmspr(SPRN_PMCR);
+       freq_data.gpstate_id = (val >> (56)) & 0xFF;
+       freq_data.pstate_id = (val >> (48)) & 0xFF;
+       if (freq_data.gpstate_id  == freq_data.pstate_id) {
+               reset_gpstates(policy);
+               spin_unlock(&gpstates->gpstate_lock);
+               return;
+       }
+
        gpstates->last_sampled_time += time_diff;
        gpstates->elapsed_time += time_diff;
-       freq_data.pstate_id = idx_to_pstate(gpstates->last_lpstate_idx);
 
-       if ((gpstates->last_gpstate_idx == gpstates->last_lpstate_idx) ||
-           (gpstates->elapsed_time > MAX_RAMP_DOWN_TIME)) {
+       if (gpstates->elapsed_time > MAX_RAMP_DOWN_TIME) {
                gpstate_idx = pstate_to_idx(freq_data.pstate_id);
                reset_gpstates(policy);
                gpstates->highest_lpstate_idx = gpstate_idx;
        } else {
+               lpstate_idx = pstate_to_idx(freq_data.pstate_id);
                gpstate_idx = calc_global_pstate(gpstates->elapsed_time,
                                                 gpstates->highest_lpstate_idx,
-                                                gpstates->last_lpstate_idx);
+                                                lpstate_idx);
        }
-
+       freq_data.gpstate_id = idx_to_pstate(gpstate_idx);
+       gpstates->last_gpstate_idx = gpstate_idx;
+       gpstates->last_lpstate_idx = lpstate_idx;
        /*
         * If local pstate is equal to global pstate, rampdown is over
         * So timer is not required to be queued.
@@ -622,10 +638,6 @@ void gpstate_timer_handler(unsigned long data)
        if (gpstate_idx != gpstates->last_lpstate_idx)
                queue_gpstate_timer(gpstates);
 
-       freq_data.gpstate_id = idx_to_pstate(gpstate_idx);
-       gpstates->last_gpstate_idx = pstate_to_idx(freq_data.gpstate_id);
-       gpstates->last_lpstate_idx = pstate_to_idx(freq_data.pstate_id);
-
        spin_unlock(&gpstates->gpstate_lock);
 
        /* Timer may get migrated to a different cpu on cpu hot unplug */
-- 
2.7.4