[HELP] How to use ftrace to learn how a function is ivoked?

[Du, ChangbinX]

Hi, All,
I have a question for ftrace usage. It is that if I have a function A, then I want to 
know how function A is ivoked?
I know ftrace can show me what sub-functions that A called by below steps:
	# echo function_graph > current_tracer
　　# echo function_A > set_graph_function
	# cat trace
Then a call stack will show what functions A has called. But sometimes I want to 
know how A is called. Is there a method to do this? Please help me!

Regards and Thanks!
Du, Changbin