On 03/19/2014 07:05 PM, Viresh Kumar wrote:
On 19 March 2014 17:45, Srivatsa S. Bhat srivatsa.bhat@linux.vnet.ibm.com wrote:
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
bool transition_ongoing; /* Tracks transition status */struct mutex transition_lock;wait_queue_head_t transition_wait;Similar to what I have done in my last version, why do you need transition_ongoing and transition_wait? Simply work with transition_lock? i.e. Acquire it for the complete transition sequence.
We *can't* acquire it for the complete transition sequence in case of drivers that do asynchronous notification, because PRECHANGE is done in one thread and POSTCHANGE is done in a totally different thread! You can't acquire a lock in one task and release it in a different task. That would be a fundamental violation of locking.
That's why I introduced the wait queue to help us create a "flow" which encompasses 2 different, but co-ordinating tasks. You simply can't do that elegantly by using plain locks alone.
Regards, Srivatsa S. Bhat