[PATCH 2/3] usb: misc: onboard_usb_hub: Add reset-gpio support

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Despite default reset upon probe, release reset line after powering up
the hub and assert reset again before powering down.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
---
My current DT node on my TQMa8MPxL looks like this
```
&usb_dwc3_1 {
	dr_mode = "host";
	#address-cells = <1>;
	#size-cells = <0>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_usbhub>;
	status = "okay";

	hub_2_0: hub@1 {
		compatible = "usb451,8142";
		reg = <1>;
		peer-hub = <&hub_3_0>;
		reset-gpio = <&gpio1 11 GPIO_ACTIVE_LOW>;
	};

	hub_3_0: hub@2 {
		compatible = "usb451,8140";
		reg = <2>;
		peer-hub = <&hub_2_0>;
		reset-gpio = <&gpio1 11 GPIO_ACTIVE_LOW>;
	};
};
```
which I don't like much for 2 reasons:
* the pinctrl has to be put in a common top-node of USB hub node. The pinctrl
  can not be requested twice.
* Apparently there is no conflict on the reset-gpio only because just one device
  gets probed here:
> $ ls /sys/bus/platform/drivers/onboard-usb-hub/
> 38200000.usb:hub@1  bind  uevent  unbind

But this seems better than to use a common fixed-regulator referenced by both
hub nodes, which just is controlled by GPIO and does not supply any voltages.
Note: It might also be necessary to add bindings to specify ramp up times and/or
reset timeouts.

 drivers/usb/misc/onboard_usb_hub.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
index 6b9b949d17d3..348fb5270266 100644
--- a/drivers/usb/misc/onboard_usb_hub.c
+++ b/drivers/usb/misc/onboard_usb_hub.c
@@ -7,6 +7,7 @@
 
 #include <linux/device.h>
 #include <linux/export.h>
+#include <linux/gpio/consumer.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
@@ -38,6 +39,7 @@ struct usbdev_node {
 struct onboard_hub {
 	struct regulator *vdd;
 	struct device *dev;
+	struct gpio_desc *reset_gpio;
 	bool always_powered_in_suspend;
 	bool is_powered_on;
 	bool going_away;
@@ -56,6 +58,10 @@ static int onboard_hub_power_on(struct onboard_hub *hub)
 		return err;
 	}
 
+	/* Deassert reset */
+	usleep_range(3000, 3100);
+	gpiod_set_value_cansleep(hub->reset_gpio, 0);
+
 	hub->is_powered_on = true;
 
 	return 0;
@@ -65,6 +71,10 @@ static int onboard_hub_power_off(struct onboard_hub *hub)
 {
 	int err;
 
+	/* Assert reset */
+	gpiod_set_value_cansleep(hub->reset_gpio, 1);
+	usleep_range(4000, 5000);
+
 	err = regulator_disable(hub->vdd);
 	if (err) {
 		dev_err(hub->dev, "failed to disable regulator: %d\n", err);
@@ -231,6 +241,14 @@ static int onboard_hub_probe(struct platform_device *pdev)
 	if (IS_ERR(hub->vdd))
 		return PTR_ERR(hub->vdd);
 
+	/* Put the hub into reset, pull reset line low, and assure 4ms reset low timing. */
+	hub->reset_gpio = devm_gpiod_get_optional(dev, "reset",
+						  GPIOD_OUT_HIGH);
+	if (IS_ERR(hub->reset_gpio))
+		return dev_err_probe(dev, PTR_ERR(hub->reset_gpio), "failed to get reset GPIO\n");
+
+	usleep_range(4000, 5000);
+
 	hub->dev = dev;
 	mutex_init(&hub->lock);
 	INIT_LIST_HEAD(&hub->udev_list);
-- 
2.25.1