trace: Track the minimum stack depth

The trace does not necessarily start at the top level, so we can see it
go negative. Track this so that we can show an accurate value for the
stack depth.

Signed-off-by: Simon Glass <sjg@chromium.org>

lib/trace.c

@@ -35,9 +35,10 @@ struct trace_hdr {
 	ulong ftrace_count;	/* Num. of ftrace records written */
 	ulong ftrace_too_deep_count;	/* Functions that were too deep */
 
-	int depth;
-	int depth_limit;
-	int max_depth;
+	int depth;		/* Depth of function calls */
+	int depth_limit;	/* Depth limit to trace to */
+	int max_depth;		/* Maximum depth seen so far */
+	int min_depth;		/* Minimum depth seen so far */
 };
 
 /* Pointer to start of trace buffer */
@@ -142,7 +143,7 @@ void notrace __cyg_profile_func_enter(void *func_ptr, void *caller)
 			hdr->untracked_count++;
 		}
 		hdr->depth++;
-		if (hdr->depth > hdr->depth_limit)
+		if (hdr->depth > hdr->max_depth)
 			hdr->max_depth = hdr->depth;
 		trace_swap_gd();
 	}
@@ -158,8 +159,10 @@ void notrace __cyg_profile_func_exit(void *func_ptr, void *caller)
 {
 	if (trace_enabled) {
 		trace_swap_gd();
-		add_ftrace(func_ptr, caller, FUNCF_EXIT);
 		hdr->depth--;
+		add_ftrace(func_ptr, caller, FUNCF_EXIT);
+		if (hdr->depth < hdr->min_depth)
+			hdr->min_depth = hdr->depth;
 		trace_swap_gd();
 	}
 }
@@ -309,8 +312,10 @@ void trace_print_stats(void)
 		printf(" (%lu dropped due to overflow)",
 		       hdr->ftrace_count - hdr->ftrace_size);
 	}
-	puts("\n");
-	printf("%15d maximum observed call depth\n", hdr->max_depth);
+
+	/* Add in minimum depth since the trace did not start at top level */
+	printf("\n%15d maximum observed call depth\n",
+	       hdr->max_depth - hdr->min_depth);
 	printf("%15d call depth limit\n", hdr->depth_limit);
 	print_grouped_ull(hdr->ftrace_too_deep_count, 10);
 	puts(" calls not traced due to depth\n");
@@ -381,8 +386,10 @@ int notrace trace_init(void *buff, size_t buff_size)
 		return -ENOSPC;
 	}
 
-	if (was_disabled)
+	if (was_disabled) {
 		memset(hdr, '\0', needed);
+		hdr->min_depth = INT_MAX;
+	}
 	hdr->func_count = func_count;
 	hdr->call_accum = (uintptr_t *)(hdr + 1);
 
@@ -427,6 +434,7 @@ int notrace trace_early_init(void)
 	memset(hdr, '\0', needed);
 	hdr->call_accum = (uintptr_t *)(hdr + 1);
 	hdr->func_count = func_count;
+	hdr->min_depth = INT_MAX;
 
 	/* Use any remaining space for the timed function trace */
 	hdr->ftrace = (struct trace_call *)((char *)hdr + needed);