PCI: imx6: Add regulator support

Some boards might require to control a regulator to power the PCIe port.

Add support for an optional regulator defined in Device Tree linked in the
PCIe controller under `vpcie-supply`.  If present, the regulator will be
disabled and then enabled as part of the PCIe host initialization process
and will be disabled when shutting down.
Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
[bhelgaas: use dev_err() instead of pr_err() in
imx6_pcie_assert_core_reset()]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Richard Zhu <hongxing.zhu@nxp.com>

Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.txt

@@ -33,6 +33,10 @@ Optional properties:
 - reset-gpio-active-high: If present then the reset sequence using the GPIO
   specified in the "reset-gpio" property is reversed (H=reset state,
   L=operation state).
+- vpcie-supply: Should specify the regulator in charge of PCIe port power.
+  The regulator will be enabled when initializing the PCIe host and
+  disabled either as part of the init process or when shutting down the
+  host.
 
 Additional required properties for imx6sx-pcie:
 - clock names: Must include the following additional entries:

drivers/pci/dwc/pci-imx6.c

@@ -24,6 +24,7 @@
 #include <linux/pci.h>
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
 #include <linux/resource.h>
 #include <linux/signal.h>
 #include <linux/types.h>
@@ -59,6 +60,7 @@ struct imx6_pcie {
 	u32			tx_swing_full;
 	u32			tx_swing_low;
 	int			link_gen;
+	struct regulator	*vpcie;
 };
 
 /* Parameters for the waiting for PCIe PHY PLL to lock on i.MX7 */
@@ -257,6 +259,8 @@ static int imx6q_pcie_abort_handler(unsigned long addr,
 
 static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
 {
+	struct device *dev = imx6_pcie->pci->dev;
+
 	switch (imx6_pcie->variant) {
 	case IMX7D:
 		reset_control_assert(imx6_pcie->pciephy_reset);
@@ -283,6 +287,14 @@ static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
 				   IMX6Q_GPR1_PCIE_REF_CLK_EN, 0 << 16);
 		break;
 	}
+
+	if (imx6_pcie->vpcie && regulator_is_enabled(imx6_pcie->vpcie) > 0) {
+		int ret = regulator_disable(imx6_pcie->vpcie);
+
+		if (ret)
+			dev_err(dev, "failed to disable vpcie regulator: %d\n",
+				ret);
+	}
 }
 
 static int imx6_pcie_enable_ref_clk(struct imx6_pcie *imx6_pcie)
@@ -349,10 +361,19 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
 	struct device *dev = pci->dev;
 	int ret;
 
+	if (imx6_pcie->vpcie && !regulator_is_enabled(imx6_pcie->vpcie)) {
+		ret = regulator_enable(imx6_pcie->vpcie);
+		if (ret) {
+			dev_err(dev, "failed to enable vpcie regulator: %d\n",
+				ret);
+			return;
+		}
+	}
+
 	ret = clk_prepare_enable(imx6_pcie->pcie_phy);
 	if (ret) {
 		dev_err(dev, "unable to enable pcie_phy clock\n");
-		return;
+		goto err_pcie_phy;
 	}
 
 	ret = clk_prepare_enable(imx6_pcie->pcie_bus);
@@ -412,6 +433,13 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
 	clk_disable_unprepare(imx6_pcie->pcie_bus);
 err_pcie_bus:
 	clk_disable_unprepare(imx6_pcie->pcie_phy);
+err_pcie_phy:
+	if (imx6_pcie->vpcie && regulator_is_enabled(imx6_pcie->vpcie) > 0) {
+		ret = regulator_disable(imx6_pcie->vpcie);
+		if (ret)
+			dev_err(dev, "failed to disable vpcie regulator: %d\n",
+				ret);
+	}
 }
 
 static void imx6_pcie_init_phy(struct imx6_pcie *imx6_pcie)
@@ -775,6 +803,13 @@ static int imx6_pcie_probe(struct platform_device *pdev)
 	if (ret)
 		imx6_pcie->link_gen = 1;
 
+	imx6_pcie->vpcie = devm_regulator_get_optional(&pdev->dev, "vpcie");
+	if (IS_ERR(imx6_pcie->vpcie)) {
+		if (PTR_ERR(imx6_pcie->vpcie) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
+		imx6_pcie->vpcie = NULL;
+	}
+
 	platform_set_drvdata(pdev, imx6_pcie);
 
 	ret = imx6_add_pcie_port(imx6_pcie, pdev);