PCI: rcar-host: Add support for optional regulators

The KingFisher board has regulators for miniPCIe, so enable these
optional regulators using devm. devm will automatically disable them
when the driver releases the device. Order variables in reverse-xmas
while we are here.

[kwilczynski: update style to match rest of the code]
Link: https://lore.kernel.org/linux-pci/20231105092908.3792-3-wsa+renesas@sang-engineering.com
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>

Author: Wolfram Sang

drivers/pci/controller/pcie-rcar-host.c

@@ -29,6 +29,7 @@
 #include <linux/phy/phy.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/regulator/consumer.h>
 
 #include "pcie-rcar.h"
 
@@ -953,14 +954,22 @@ static const struct of_device_id rcar_pcie_of_match[] = {
 	{},
 };
 
+/* Design note 346 from Linear Technology says order is not important. */
+static const char * const rcar_pcie_supplies[] = {
+	"vpcie1v5",
+	"vpcie3v3",
+	"vpcie12v",
+};
+
 static int rcar_pcie_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
+	struct pci_host_bridge *bridge;
 	struct rcar_pcie_host *host;
 	struct rcar_pcie *pcie;
+	unsigned int i;
 	u32 data;
 	int err;
-	struct pci_host_bridge *bridge;
 
 	bridge = devm_pci_alloc_host_bridge(dev, sizeof(*host));
 	if (!bridge)
@@ -971,6 +980,13 @@ static int rcar_pcie_probe(struct platform_device *pdev)
 	pcie->dev = dev;
 	platform_set_drvdata(pdev, host);
 
+	for (i = 0; i < ARRAY_SIZE(rcar_pcie_supplies); i++) {
+		err = devm_regulator_get_enable_optional(dev, rcar_pcie_supplies[i]);
+		if (err < 0 && err != -ENODEV)
+			return dev_err_probe(dev, err, "failed to enable regulator: %s\n",
+					     rcar_pcie_supplies[i]);
+	}
+
 	pm_runtime_enable(pcie->dev);
 	err = pm_runtime_get_sync(pcie->dev);
 	if (err < 0) {