[PATCH v2 03/22] pinctrl: pinctrl-generic: Make the "function" property optional

[Changhuang Liang <changhuang.liang@starfivetech.com>]

Some pinctrl subnodes only need to configure pin properties (e.g.,
power-source, bias, drive strength) without assigning any mux function.

Currently, the driver requires a valid "function" property for all
pinctrl subnodes. This forces the addition of dummy or redundant
"function" entries when only pin configuration is needed.

Example use case:
gpios-configs {
    config {
        pins = <0 1 2 3>;
        power-source = <0>;
    };
};

Make the "function" property optional. If it is missing, skip adding
the mux map and only process the pin configuration.

Signed-off-by: Changhuang Liang <changhuang.liang@starfivetech.com>
---
 drivers/pinctrl/pinctrl-generic.c | 37 ++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/drivers/pinctrl/pinctrl-generic.c b/drivers/pinctrl/pinctrl-generic.c
index efb39c6a6703..c7dd0924aa0e 100644
--- a/drivers/pinctrl/pinctrl-generic.c
+++ b/drivers/pinctrl/pinctrl-generic.c
@@ -62,19 +62,36 @@ static int pinctrl_generic_pins_function_dt_subnode_to_map(struct pinctrl_dev *p
 
 		pins[i] = pin;
 
-		ret = of_property_read_string(np, "function", &functions[i]);
-		if (ret)
-			return ret;
+		if (functions) {
+			ret = of_property_read_string(np, "function", &functions[i]);
+			if (ret < 0) {
+				/* EINVAL = missing, which is fine since it's optional */
+				if (ret != -EINVAL) {
+					dev_err(dev, "%pOF: could not parse property function\n",
+						np);
+					return ret;
+				}
+
+				devm_kfree(dev, functions);
+				functions = NULL;
+
+				/* Continue parsing all pins */
+				continue;
+			}
+		}
 	}
 
-	ret = pinctrl_utils_reserve_map(pctldev, maps, num_reserved_maps, num_maps, reserve);
-	if (ret)
-		return ret;
+	if (functions) {
+		ret = pinctrl_utils_reserve_map(pctldev, maps, num_reserved_maps,
+						num_maps, reserve);
+		if (ret)
+			return ret;
 
-	ret = pinctrl_utils_add_map_mux(pctldev, maps, num_reserved_maps, num_maps, group_name,
-					parent->name);
-	if (ret < 0)
-		return ret;
+		ret = pinctrl_utils_add_map_mux(pctldev, maps, num_reserved_maps,
+						num_maps, group_name, parent->name);
+		if (ret < 0)
+			return ret;
+	}
 
 	ret = pinctrl_generic_add_group(pctldev, group_name, pins, npins, functions);
 	if (ret < 0)
-- 
2.25.1