[review] drivers: regulator: print regulator tree summary

Beautify (IMHO) the regulator tree:
- remove empty lines between root supplies. They are now prefixed
  with indentation string "o- ";
- prevent bars '|' when last node of a supply was already printed
- use `-- for last supplied of a supply and |-- otherwise.

For example, the below tree:

I/TC: Regulator tree summary
I/TC:
I/TC: vin       (...)
I/TC: +-- vdd_sd        (...)
I/TC: +-- vdd_usb       (...)
I/TC: |   +-- usb33     (...)
I/TC: |   |   +-- usb33_io     (...)
I/TC: +-- vdd_adc       (...)
I/TC: +-- vddcore       (...)
I/TC: +-- vdd   (...)
I/TC: |   +-- reg11     (...)
I/TC: |   +-- reg18     (...)
I/TC:
I/TC: v3v3_ao   (...)
I/TC: +-- v3v3_sw       (...)
I/TC:

is now printed as:
I/TC: Regulator tree summary
I/TC:
I/TC: o- vin       (...)
I/TC:    |-- vdd_sd        (...)
I/TC:    |-- vdd_usb       (...)
I/TC:    |   `-- usb33     (...)
I/TC:    |       `-- usb33_io     (...)
I/TC:    |-- vdd_adc       (...)
I/TC:    |-- vddcore       (...)
I/TC:    `-- vdd   (...)
I/TC:        |-- reg11     (...)
I/TC:        `-- reg18     (...)
I/TC:
I/TC: o- v3v3_ao   (...)
I/TC:    `-- v3v3_sw       (...)
I/TC:

Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>

core/drivers/regulator/regulator.c

@@ -328,6 +328,43 @@ static __printf(3, 4) char *add_msg(char *cur, char *end, const char *fmt, ...)
 	return cur + ret;
 }
 
+/* Regulator is the last supplied one by its supply in the registered list */
+static bool regulator_is_supply_last_supplied(struct regulator *node_regulator)
+{
+	struct regulator *regulator = NULL;
+
+	/* Find if there is still another node with the same parent */
+	regulator = SLIST_NEXT(node_regulator, link);
+	while (regulator && regulator->supply != node_regulator->supply)
+		regulator = SLIST_NEXT(regulator, link);
+
+	return !regulator;
+}
+
+/* Supply last node may already be printed for indentation level @cur_indent */
+static bool indent_with_empty_string(struct regulator *node_regulator,
+				     int node_indent, int cur_indent)
+{
+	struct regulator *indent_plus_one_regulator = NULL;
+	struct regulator *indent_regulator = NULL;
+	struct regulator *regulator = NULL;
+	int indent = 0;
+
+	/* Find the supplied and supply of @cur_indent indentation level */
+	indent_regulator = node_regulator;
+	for (indent = 0; indent < node_indent - cur_indent; indent++) {
+		indent_plus_one_regulator = indent_regulator;
+		indent_regulator = indent_regulator->supply;
+	}
+
+	/* Find if there remains a supplied regulator for the found supply */
+	regulator = SLIST_NEXT(indent_plus_one_regulator, link);
+	while (regulator && regulator->supply != indent_regulator)
+		regulator = SLIST_NEXT(regulator, link);
+
+	return !regulator;
+}
+
 static void __maybe_unused print_regulator(struct regulator *regulator,
 					   int indent)
 {
@@ -345,15 +382,32 @@ static void __maybe_unused print_regulator(struct regulator *regulator,
 	int n = 0;
 
 	if (indent) {
+		/* Indent for root clock level */
+		msg = add_msg(msg, msg_end, "   ");
+		if (!msg)
+			goto out;
+
+		/* Indent for root supply to regulator supply levels */
 		for (n = 0; n < indent - 1; n++) {
-			msg = add_msg(msg, msg_end, "|   ");
+			if (indent_with_empty_string(regulator, indent, n))
+				msg = add_msg(msg, msg_end, "    ");
+			else
+				msg = add_msg(msg, msg_end, "|   ");
 			if (!msg)
 				goto out;
 		}
 
-		msg = add_msg(msg, msg_end, "+-- ");
+		/* Regulator indentation */
+		if (regulator_is_supply_last_supplied(regulator))
+			msg = add_msg(msg, msg_end, "`-- ");
+		else
+			msg = add_msg(msg, msg_end, "|-- ");
+
 		if (!msg)
 			goto out;
+	} else {
+		/* Root supply indentation */
+		msg = add_msg(msg, msg_end, "o- ");
 	}
 
 	regulator_get_range(regulator, &level_min, &level_max);