PCI: armada8k: Add support for gpio controlled reset signal

Add support for the gpio reset signal binding as described in the
designware-pcie.txt DT binding document. Both the documented
'reset-gpio' property name and the more standard 'reset-gpios' name are
supported.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

drivers/pci/controller/dwc/pcie-armada8k.c

@@ -22,6 +22,7 @@
 #include <linux/resource.h>
 #include <linux/of_pci.h>
 #include <linux/of_irq.h>
+#include <linux/gpio/consumer.h>
 
 #include "pcie-designware.h"
 
@@ -29,6 +30,7 @@ struct armada8k_pcie {
 	struct dw_pcie *pci;
 	struct clk *clk;
 	struct clk *clk_reg;
+	struct gpio_desc *reset_gpio;
 };
 
 #define PCIE_VENDOR_REGS_OFFSET		0x8000
@@ -137,6 +139,12 @@ static int armada8k_pcie_host_init(struct pcie_port *pp)
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
 	struct armada8k_pcie *pcie = to_armada8k_pcie(pci);
 
+	if (pcie->reset_gpio) {
+		/* assert and then deassert the reset signal */
+		gpiod_set_value_cansleep(pcie->reset_gpio, 1);
+		msleep(100);
+		gpiod_set_value_cansleep(pcie->reset_gpio, 0);
+	}
 	dw_pcie_setup_rc(pp);
 	armada8k_pcie_establish_link(pcie);
 
@@ -249,6 +257,14 @@ static int armada8k_pcie_probe(struct platform_device *pdev)
 		goto fail_clkreg;
 	}
 
+	/* Get reset gpio signal and hold asserted (logically high) */
+	pcie->reset_gpio = devm_gpiod_get_optional(dev, "reset",
+						   GPIOD_OUT_HIGH);
+	if (IS_ERR(pcie->reset_gpio)) {
+		ret = PTR_ERR(pcie->reset_gpio);
+		goto fail_clkreg;
+	}
+
 	platform_set_drvdata(pdev, pcie);
 
 	ret = armada8k_add_pcie_port(pcie, pdev);