pinctrl: spear: plgpio: Introduce regmap phandle

Resources need to be shared between pinmux and plgpio.

Introduce regmap phandle in order to retrieve the regmap
from the phandle if the property is present.
This allows to retrieve an external regmap (ie the one
used by pinmux if the phandle references the pinmux node)
from plgpio.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20211202095255.165797-4-herve.codina@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/spear/pinctrl-plgpio.c

@@ -523,18 +523,30 @@ static int plgpio_probe_dt(struct platform_device *pdev, struct plgpio *plgpio)
 
 static int plgpio_probe(struct platform_device *pdev)
 {
+	struct device_node *regmap_np;
 	struct plgpio *plgpio;
 	int ret, irq;
 
 	plgpio = devm_kzalloc(&pdev->dev, sizeof(*plgpio), GFP_KERNEL);
 	if (!plgpio)
 		return -ENOMEM;
 
-	plgpio->regmap = device_node_to_regmap(pdev->dev.of_node);
-	if (IS_ERR(plgpio->regmap)) {
-		dev_err(&pdev->dev, "Init regmap failed (%pe)\n",
-			plgpio->regmap);
-		return PTR_ERR(plgpio->regmap);
+	regmap_np = of_parse_phandle(pdev->dev.of_node, "regmap", 0);
+	if (regmap_np) {
+		plgpio->regmap = device_node_to_regmap(regmap_np);
+		of_node_put(regmap_np);
+		if (IS_ERR(plgpio->regmap)) {
+			dev_err(&pdev->dev, "Retrieve regmap failed (%pe)\n",
+				plgpio->regmap);
+			return PTR_ERR(plgpio->regmap);
+		}
+	} else {
+		plgpio->regmap = device_node_to_regmap(pdev->dev.of_node);
+		if (IS_ERR(plgpio->regmap)) {
+			dev_err(&pdev->dev, "Init regmap failed (%pe)\n",
+				plgpio->regmap);
+			return PTR_ERR(plgpio->regmap);
+		}
 	}
 
 	ret = plgpio_probe_dt(pdev, plgpio);