[RFC PATCH 1/1] usb: dwc3: of-simple: Add extcon support

[Prashant Malani]

Add optional extcon notifier support to enable the hotplug / unplug of
the underlying PHY layer devices.

If supported, the Device Tree (DT) node for the device should include an
"extcon" property which is a phandle to an extcon DT node.

This patch is an effort to incorporate the equivalent support from the
Rockchip dwc3 driver implementation from Chrome OS [1] to the mainline.

[1] : https://chromium.googlesource.com/chromiumos/third_party/kernel/
+/refs/heads/chromeos-4.4/drivers/usb/dwc3/dwc3-rockchip.c

Cc: Benson Leung <bleung@xxxxxxxxxxxx>
Cc: Guenter Roeck <groeck@xxxxxxxxxxxx>
Cc: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
Signed-off-by: Prashant Malani <pmalani@xxxxxxxxxxxx>
---
 drivers/usb/dwc3/dwc3-of-simple.c | 149 +++++++++++++++++++++++++++++-
 1 file changed, 146 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/dwc3/dwc3-of-simple.c b/drivers/usb/dwc3/dwc3-of-simple.c
index e64754be47b4..28bde27cd1f9 100644
--- a/drivers/usb/dwc3/dwc3-of-simple.c
+++ b/drivers/usb/dwc3/dwc3-of-simple.c
@@ -11,6 +11,7 @@
  * by Subbaraya Sundeep Bhatta <subbaraya.sundeep.bhatta@xxxxxxxxxx>
  */
 
+#include <linux/extcon.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
@@ -29,8 +30,117 @@ struct dwc3_of_simple {
 	struct reset_control	*resets;
 	bool			pulse_resets;
 	bool			need_reset;
+	struct extcon_dev	*edev;
+	struct notifier_block	nb;
+	struct work_struct	work;
+	/* Denotes whether child devices have been populated. */
+	bool			populated;
+	bool			suspended;
+	spinlock_t		suspend_lock;
 };
 
+static int dwc3_of_simple_populate(struct dwc3_of_simple *simple)
+{
+	struct device *dev = simple->dev;
+	struct device_node *np = dev->of_node;
+	int ret;
+
+	ret = of_platform_populate(np, NULL, NULL, dev);
+	if (ret) {
+		dev_err(dev, "Failed to populate dwc3 devices.\n");
+		return ret;
+	}
+	simple->populated = true;
+	return 0;
+}
+
+static void dwc3_of_simple_depopulate(struct dwc3_of_simple *simple)
+{
+	if (simple->populated) {
+		of_platform_depopulate(simple->dev);
+		simple->populated = false;
+	}
+}
+
+static void dwc3_of_simple_work(struct work_struct *work)
+{
+	struct dwc3_of_simple *simple = container_of(work,
+					struct dwc3_of_simple, work);
+	struct extcon_dev *edev = simple->edev;
+
+	if (extcon_get_state(edev, EXTCON_USB_HOST) > 0) {
+		if (simple->populated)
+			return;
+
+		dwc3_of_simple_populate(simple);
+	} else {
+		if (!simple->populated)
+			return;
+
+		dwc3_of_simple_depopulate(simple);
+	}
+}
+
+static int dwc3_of_simple_notifier(struct notifier_block *nb,
+			      unsigned long event, void *ptr)
+{
+	struct dwc3_of_simple *simple = container_of(nb, struct dwc3_of_simple,
+						nb);
+	unsigned long flags;
+
+	spin_lock_irqsave(&simple->suspend_lock, flags);
+	if (!simple->suspended)
+		schedule_work(&simple->work);
+	spin_unlock_irqrestore(&simple->suspend_lock, flags);
+
+	return NOTIFY_OK;
+}
+
+static int dwc3_of_simple_extcon_register(struct dwc3_of_simple *simple)
+{
+	struct device		*dev = simple->dev;
+	struct extcon_dev	*edev;
+	int			ret;
+
+	edev = extcon_get_edev_by_phandle(dev, 0);
+	if (IS_ERR(edev)) {
+		/* The extcon property is optional. */
+		if (PTR_ERR(edev) == -ENODEV)
+			return 0;
+		if (PTR_ERR(edev) != -EPROBE_DEFER)
+			dev_err(dev, "Couldn't get extcon device.\n");
+		return PTR_ERR(edev);
+	}
+
+	INIT_WORK(&simple->work, dwc3_of_simple_work);
+
+	simple->nb.notifier_call = dwc3_of_simple_notifier;
+	ret = devm_extcon_register_notifier(dev, edev, EXTCON_USB_HOST,
+					&simple->nb);
+	if (ret < 0) {
+		dev_err(dev, "Failed to register notifier.\n");
+		return ret;
+	}
+
+	simple->edev = edev;
+
+	return 0;
+}
+
+static void dwc3_of_simple_extcon_unregister(struct dwc3_of_simple *simple)
+{
+	if (!simple->edev)
+		return;
+
+	/*
+	 * We explicitly unregister the notifier to prevent races with
+	 * the of_depopulate() call in remove().
+	 */
+	devm_extcon_unregister_notifier(simple->dev, simple->edev,
+					EXTCON_USB_HOST, &simple->nb);
+	cancel_work_sync(&simple->work);
+}
+
 static int dwc3_of_simple_probe(struct platform_device *pdev)
 {
 	struct dwc3_of_simple	*simple;
@@ -47,6 +157,8 @@ static int dwc3_of_simple_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, simple);
 	simple->dev = dev;
 
+	spin_lock_init(&simple->suspend_lock);
+
 	/*
 	 * Some controllers need to toggle the usb3-otg reset before trying to
 	 * initialize the PHY, otherwise the PHY times out.
@@ -87,9 +199,24 @@ static int dwc3_of_simple_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_resetc_assert;
 
-	ret = of_platform_populate(np, NULL, NULL, dev);
-	if (ret)
+	ret = dwc3_of_simple_extcon_register(simple);
+	if (ret < 0) {
+		dev_warn(dev, "No extcon device found, err: %d\n", ret);
 		goto err_clk_put;
+	}
+
+	if (!simple->edev) {
+		ret = dwc3_of_simple_populate(simple);
+		if (ret)
+			goto err_clk_put;
+	} else {
+		/*
+		 * Populate through worker to avoid race conditions against
+		 * action scheduled through notifier.
+		 */
+		if (extcon_get_state(simple->edev, EXTCON_USB_HOST) > 0)
+			schedule_work(&simple->work);
+	}
 
 	pm_runtime_set_active(dev);
 	pm_runtime_enable(dev);
@@ -112,7 +239,8 @@ static int dwc3_of_simple_probe(struct platform_device *pdev)
 
 static void __dwc3_of_simple_teardown(struct dwc3_of_simple *simple)
 {
-	of_platform_depopulate(simple->dev);
+	dwc3_of_simple_extcon_unregister(simple);
+	dwc3_of_simple_depopulate(simple);
 
 	clk_bulk_disable_unprepare(simple->num_clocks, simple->clks);
 	clk_bulk_put_all(simple->num_clocks, simple->clks);
@@ -163,6 +291,13 @@ static int __maybe_unused dwc3_of_simple_runtime_resume(struct device *dev)
 static int __maybe_unused dwc3_of_simple_suspend(struct device *dev)
 {
 	struct dwc3_of_simple *simple = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&simple->suspend_lock, flags);
+	simple->suspended = true;
+	spin_unlock_irqrestore(&simple->suspend_lock, flags);
+
+	cancel_work_sync(&simple->work);
 
 	if (simple->need_reset)
 		reset_control_assert(simple->resets);
@@ -173,10 +308,18 @@ static int __maybe_unused dwc3_of_simple_suspend(struct device *dev)
 static int __maybe_unused dwc3_of_simple_resume(struct device *dev)
 {
 	struct dwc3_of_simple *simple = dev_get_drvdata(dev);
+	unsigned long flags;
 
 	if (simple->need_reset)
 		reset_control_deassert(simple->resets);
 
+	spin_lock_irqsave(&simple->suspend_lock, flags);
+	simple->suspended = false;
+	spin_unlock_irqrestore(&simple->suspend_lock, flags);
+
+	if (simple->edev)
+		schedule_work(&simple->work);
+
 	return 0;
 }
 
-- 
2.27.0.rc0.183.gde8f92d652-goog