clk: Add trace events for rate requests

It is currently fairly difficult to follow what clk_rate_request are
issued, and how they have been modified once done.

Indeed, there's multiple paths that can be taken, some functions are
recursive and will just forward the request to its parent, etc.

Adding a lot of debug prints is just not very convenient, so let's add
trace events for the clock requests, one before they are submitted and
one after they are returned.

That way we can simply toggle the tracing on without modifying the
kernel code and without affecting performances or the kernel logs too
much.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20221018-clk-rate-request-tracing-v2-2-5170b363c413@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk.c

@@ -603,10 +603,15 @@ int clk_mux_determine_rate_flags(struct clk_hw *hw,
 			}
 
 			clk_core_forward_rate_req(core, req, parent, &parent_req, req->rate);
+
+			trace_clk_rate_request_start(&parent_req);
+
 			ret = clk_core_round_rate_nolock(parent, &parent_req);
 			if (ret)
 				return ret;
 
+			trace_clk_rate_request_done(&parent_req);
+
 			best = parent_req.rate;
 		} else if (parent) {
 			best = clk_core_get_rate_nolock(parent);
@@ -630,10 +635,15 @@ int clk_mux_determine_rate_flags(struct clk_hw *hw,
 			struct clk_rate_request parent_req;
 
 			clk_core_forward_rate_req(core, req, parent, &parent_req, req->rate);
+
+			trace_clk_rate_request_start(&parent_req);
+
 			ret = clk_core_round_rate_nolock(parent, &parent_req);
 			if (ret)
 				continue;
 
+			trace_clk_rate_request_done(&parent_req);
+
 			parent_rate = parent_req.rate;
 		} else {
 			parent_rate = clk_core_get_rate_nolock(parent);
@@ -1547,10 +1557,15 @@ static int clk_core_round_rate_nolock(struct clk_core *core,
 		struct clk_rate_request parent_req;
 
 		clk_core_forward_rate_req(core, req, core->parent, &parent_req, req->rate);
+
+		trace_clk_rate_request_start(&parent_req);
+
 		ret = clk_core_round_rate_nolock(core->parent, &parent_req);
 		if (ret)
 			return ret;
 
+		trace_clk_rate_request_done(&parent_req);
+
 		req->best_parent_rate = parent_req.rate;
 		req->rate = parent_req.rate;
 
@@ -1601,10 +1616,14 @@ unsigned long clk_hw_round_rate(struct clk_hw *hw, unsigned long rate)
 
 	clk_core_init_rate_req(hw->core, &req, rate);
 
+	trace_clk_rate_request_start(&req);
+
 	ret = clk_core_round_rate_nolock(hw->core, &req);
 	if (ret)
 		return 0;
 
+	trace_clk_rate_request_done(&req);
+
 	return req.rate;
 }
 EXPORT_SYMBOL_GPL(clk_hw_round_rate);
@@ -1633,8 +1652,12 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
 
 	clk_core_init_rate_req(clk->core, &req, rate);
 
+	trace_clk_rate_request_start(&req);
+
 	ret = clk_core_round_rate_nolock(clk->core, &req);
 
+	trace_clk_rate_request_done(&req);
+
 	if (clk->exclusive_count)
 		clk_core_rate_protect(clk->core);
 
@@ -2126,10 +2149,14 @@ static struct clk_core *clk_calc_new_rates(struct clk_core *core,
 
 		clk_core_init_rate_req(core, &req, rate);
 
+		trace_clk_rate_request_start(&req);
+
 		ret = clk_core_determine_round_nolock(core, &req);
 		if (ret < 0)
 			return NULL;
 
+		trace_clk_rate_request_done(&req);
+
 		best_parent_rate = req.best_parent_rate;
 		new_rate = req.rate;
 		parent = req.best_parent_hw ? req.best_parent_hw->core : NULL;
@@ -2325,8 +2352,12 @@ static unsigned long clk_core_req_round_rate_nolock(struct clk_core *core,
 
 	clk_core_init_rate_req(core, &req, req_rate);
 
+	trace_clk_rate_request_start(&req);
+
 	ret = clk_core_round_rate_nolock(core, &req);
 
+	trace_clk_rate_request_done(&req);
+
 	/* restore the protection */
 	clk_core_rate_restore_protect(core, cnt);
 

include/trace/events/clk.h

@@ -264,6 +264,49 @@ DEFINE_EVENT(clk_duty_cycle, clk_set_duty_cycle_complete,
 	TP_ARGS(core, duty)
 );
 
+DECLARE_EVENT_CLASS(clk_rate_request,
+
+	TP_PROTO(struct clk_rate_request *req),
+
+	TP_ARGS(req),
+
+	TP_STRUCT__entry(
+		__string(        name, req->core ? req->core->name : "none")
+		__string(       pname, req->best_parent_hw ? clk_hw_get_name(req->best_parent_hw) : "none" )
+		__field(unsigned long,           min                       )
+		__field(unsigned long,           max                       )
+		__field(unsigned long,           prate                     )
+	),
+
+	TP_fast_assign(
+		__assign_str(name, req->core ? req->core->name : "none");
+		__assign_str(pname, req->best_parent_hw ? clk_hw_get_name(req->best_parent_hw) : "none");
+		__entry->min = req->min_rate;
+		__entry->max = req->max_rate;
+		__entry->prate = req->best_parent_rate;
+	),
+
+	TP_printk("%s min %lu max %lu, parent %s (%lu)", __get_str(name),
+		  (unsigned long)__entry->min,
+		  (unsigned long)__entry->max,
+		  __get_str(pname),
+		  (unsigned long)__entry->prate)
+);
+
+DEFINE_EVENT(clk_rate_request, clk_rate_request_start,
+
+	TP_PROTO(struct clk_rate_request *req),
+
+	TP_ARGS(req)
+);
+
+DEFINE_EVENT(clk_rate_request, clk_rate_request_done,
+
+	TP_PROTO(struct clk_rate_request *req),
+
+	TP_ARGS(req)
+);
+
 #endif /* _TRACE_CLK_H */
 
 /* This part must be outside protection */