[PATCH v8 3/3] usb: dwc3: xilinx: Add ULPI PHY reset handling

[Robert Hancock <robert.hancock@calian.com>]

Hook up an optional GPIO-based reset for the connected USB ULPI PHY
device. This is typically already done by the first-stage boot loader,
however it can be more robust to ensure this reset is done prior to
loading the driver in Linux.

Based on a patch "usb: dwc3: xilinx: Add gpio-reset support" in the
Xilinx kernel tree by Piyush Mehta <piyush.mehta@xilinx.com>.

Signed-off-by: Robert Hancock <robert.hancock@calian.com>
---
 drivers/usb/dwc3/dwc3-xilinx.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
index a6f3a9b38789..1ee6011ada44 100644
--- a/drivers/usb/dwc3/dwc3-xilinx.c
+++ b/drivers/usb/dwc3/dwc3-xilinx.c
@@ -11,6 +11,7 @@
 #include <linux/slab.h>
 #include <linux/clk.h>
 #include <linux/of.h>
+#include <linux/gpio/consumer.h>
 #include <linux/platform_device.h>
 #include <linux/dma-mapping.h>
 #include <linux/of_platform.h>
@@ -101,6 +102,7 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
 	struct phy		*usb3_phy;
 	int			ret = 0;
 	u32			reg;
+	struct gpio_desc        *reset_gpio;
 
 	usb3_phy = devm_phy_optional_get(dev, "usb3-phy");
 	if (IS_ERR(usb3_phy)) {
@@ -110,6 +112,14 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
 		goto err;
 	}
 
+	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(reset_gpio)) {
+		ret = PTR_ERR(reset_gpio);
+		dev_err_probe(dev, ret,
+			      "Failed to get reset gpio\n");
+		goto err;
+	}
+
 	/*
 	 * The following core resets are not required unless a USB3 PHY
 	 * is used, and the subsequent register settings are not required
@@ -201,6 +211,15 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
 	}
 
 skip_usb3_phy:
+	/* ulpi reset via gpio-modepin or gpio-framework driver */
+	if (reset_gpio) {
+		/* Toggle ulpi to reset the phy. */
+		gpiod_set_value(reset_gpio, 0);
+		usleep_range(5000, 10000); /* delay */
+		gpiod_set_value(reset_gpio, 1);
+		usleep_range(5000, 10000); /* delay */
+	}
+
 	/*
 	 * This routes the USB DMA traffic to go through FPD path instead
 	 * of reaching DDR directly. This traffic routing is needed to
-- 
2.31.1