[PATCH 2/2] usb: dwc3: xilinx: Add gpio-reset support

[Piyush Mehta <piyush.mehta@xilinx.com>]

This patch adds a USB GPIO based reset for dwc3-xilinx driver. The PHY
needs to be reset after the completion of phy initialization. As part
of the reset, check for gpio-reset binding before toggling the pin.
This feature is advantageous when the user toggle GPIO to trigger the
ULPI-PHY reset.

Delay of milliseconds is added in between low and high to meet the setup
and hold time requirement of the reset. The reset-gpio error handling is
added for error notification.

Some GPIO controllers must be accessed using message-based buses, like
I2C or SPI, to address this problem, updates GPIO access with sleep API.

This reset is specific to the zynqMp.

Signed-off-by: Piyush Mehta <piyush.mehta@xilinx.com>
---
 drivers/usb/dwc3/dwc3-xilinx.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
index a6f3a9b..67b237c 100644
--- a/drivers/usb/dwc3/dwc3-xilinx.c
+++ b/drivers/usb/dwc3/dwc3-xilinx.c
@@ -13,6 +13,7 @@
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/dma-mapping.h>
+#include <linux/of_gpio.h>
 #include <linux/of_platform.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
@@ -98,6 +99,7 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
 {
 	struct device		*dev = priv_data->dev;
 	struct reset_control	*crst, *hibrst, *apbrst;
+	struct gpio_desc	*reset_gpio;
 	struct phy		*usb3_phy;
 	int			ret = 0;
 	u32			reg;
@@ -201,6 +203,21 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
 	}
 
 skip_usb3_phy:
+	/* ulpi reset via gpio-modepin or gpio-framework driver */
+	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(reset_gpio)) {
+		return dev_err_probe(dev, PTR_ERR(reset_gpio),
+				     "Failed to request reset GPIO\n");
+	}
+
+	if (reset_gpio) {
+		/* Toggle ulpi to reset the phy. */
+		gpiod_set_value_cansleep(reset_gpio, 1);
+		usleep_range(5000, 10000);
+		gpiod_set_value_cansleep(reset_gpio, 0);
+		usleep_range(5000, 10000);
+	}
+
 	/*
 	 * This routes the USB DMA traffic to go through FPD path instead
 	 * of reaching DDR directly. This traffic routing is needed to
-- 
2.7.4