[RFC][PATCH v2 05/13] usb: otg: add OTG core

[Roger Quadros]

The OTG core instantiates the OTG Finite State Machine
per OTG controller and manages starting/stopping the
host and gadget controllers based on the bus state.

It provides APIs for the following tasks

- Registering an OTG capable controller
- Registering Host and Gadget controllers to OTG core
- Providing inputs to and kicking the OTG state machine

TODO:
- sysfs interface to allow application inputs to OTG state machine
- otg class?

Signed-off-by: Roger Quadros <rogerq@xxxxxx>
---
 drivers/usb/Makefile         |   1 +
 drivers/usb/common/Makefile  |   1 +
 drivers/usb/common/usb-otg.c | 743 +++++++++++++++++++++++++++++++++++++++++++
 drivers/usb/common/usb-otg.h |  71 +++++
 drivers/usb/core/Kconfig     |   8 +
 include/linux/usb/usb-otg.h  |  94 ++++++
 6 files changed, 918 insertions(+)
 create mode 100644 drivers/usb/common/usb-otg.c
 create mode 100644 drivers/usb/common/usb-otg.h
 create mode 100644 include/linux/usb/usb-otg.h

diff --git a/drivers/usb/Makefile b/drivers/usb/Makefile
index 2f1e2aa..07f59a5 100644
--- a/drivers/usb/Makefile
+++ b/drivers/usb/Makefile
@@ -60,5 +60,6 @@ obj-$(CONFIG_USB_RENESAS_USBHS)	+= renesas_usbhs/
 obj-$(CONFIG_USB_GADGET)	+= gadget/
 
 obj-$(CONFIG_USB_COMMON)	+= common/
+obj-$(CONFIG_USB_OTG_CORE)	+= common/
 
 obj-$(CONFIG_USBIP_CORE)	+= usbip/
diff --git a/drivers/usb/common/Makefile b/drivers/usb/common/Makefile
index ca2f8bd..573fc75 100644
--- a/drivers/usb/common/Makefile
+++ b/drivers/usb/common/Makefile
@@ -7,3 +7,4 @@ usb-common-y			  += common.o
 usb-common-$(CONFIG_USB_LED_TRIG) += led.o
 
 obj-$(CONFIG_USB_OTG_FSM) += usb-otg-fsm.o
+obj-$(CONFIG_USB_OTG_CORE) += usb-otg.o
diff --git a/drivers/usb/common/usb-otg.c b/drivers/usb/common/usb-otg.c
new file mode 100644
index 0000000..e848e08
--- /dev/null
+++ b/drivers/usb/common/usb-otg.c
@@ -0,0 +1,743 @@
+/**
+ * drivers/usb/common/usb-otg.c - USB OTG core
+ *
+ * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com
+ * Author: Roger Quadros <rogerq@xxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/ktime.h>
+#include <linux/hrtimer.h>
+#include <linux/list.h>
+#include <linux/usb/otg.h>
+#include <linux/usb/phy.h>	/* enum usb_otg_state */
+#include <linux/usb/gadget.h>
+#include <linux/usb/usb-otg.h>
+#include <linux/workqueue.h>
+
+#include "usb-otg.h"
+
+/* to link timer with callback data */
+struct otg_timer {
+	struct hrtimer timer;
+	ktime_t timeout;
+	/* callback data */
+	int *timeout_bit;
+	struct otg_data *otgd;
+};
+
+struct otg_hcd {
+	struct usb_hcd *hcd;
+	unsigned int irqnum;
+	unsigned long irqflags;
+};
+
+struct otg_data {
+	struct device *dev;	/* HCD & GCD's parent device */
+
+	struct otg_fsm fsm;
+	/* HCD, GCD and usb_otg_state are present in otg_fsm->otg
+	 * HCD is bus_to_hcd(fsm->otg->host)
+	 * GCD is fsm->otg->gadget
+	 */
+	struct otg_fsm_ops fsm_ops;	/* private copy for override */
+	struct usb_otg otg;		/* allocator for fsm->otg */
+
+	struct otg_hcd primary_hcd;
+	struct otg_hcd shared_hcd;
+
+	/* saved hooks to OTG device */
+	int (*start_host)(struct otg_fsm *fsm, int on);
+	int (*start_gadget)(struct otg_fsm *fsm, int on);
+
+	struct list_head list;
+
+	struct work_struct work;	/* OTG FSM work */
+	struct workqueue_struct *wq;
+
+	struct otg_timer timers[NUM_OTG_FSM_TIMERS];
+
+	bool fsm_running;
+	/* use otg->fsm.lock for serializing access */
+};
+
+/* OTG device list */
+LIST_HEAD(otg_list);
+static DEFINE_MUTEX(otg_list_mutex);
+
+/**
+ * check if device is in our OTG list and return
+ * otg_data, else NULL.
+ *
+ * otg_list_mutex must be held.
+ */
+static struct otg_data *usb_otg_device_get_otgd(struct device *parent_dev)
+{
+	struct otg_data *otgd;
+
+	list_for_each_entry(otgd, &otg_list, list) {
+		if (otgd->dev == parent_dev)
+			return otgd;
+	}
+
+	return NULL;
+}
+
+/**
+ * timer callback to set timeout bit and kick FSM
+ */
+static enum hrtimer_restart set_tmout(struct hrtimer *data)
+{
+	struct otg_timer *otgtimer;
+
+	otgtimer = container_of(data, struct otg_timer, timer);
+	if (otgtimer->timeout_bit)
+		*otgtimer->timeout_bit = 1;
+
+	usb_otg_sync_inputs(&otgtimer->otgd->fsm);
+
+	return HRTIMER_NORESTART;
+}
+
+/**
+ * Initialize one OTG timer with callback, timeout and timeout bit
+ */
+static void otg_timer_init(enum otg_fsm_timer id, struct otg_data *otgd,
+			   enum hrtimer_restart (*callback)(struct hrtimer *),
+			   unsigned long expires_ms,
+			   int *timeout_bit)
+{
+	struct otg_timer *otgtimer = &otgd->timers[id];
+	struct hrtimer *timer = &otgtimer->timer;
+
+	otgtimer->timeout = ms_to_ktime(expires_ms);
+	hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	timer->function = callback;
+
+	otgtimer->timeout_bit = timeout_bit;
+	otgtimer->otgd = otgd;
+}
+
+/**
+ * Initialize standard OTG timers
+ */
+static void usb_otg_init_timers(struct otg_data *otgd)
+{
+	struct otg_fsm *fsm = &otgd->fsm;
+
+	otg_timer_init(A_WAIT_VRISE, otgd, set_tmout, TA_WAIT_VRISE, &fsm->a_wait_vrise_tmout);
+	otg_timer_init(A_WAIT_VFALL, otgd, set_tmout, TA_WAIT_VFALL, &fsm->a_wait_vfall_tmout);
+	otg_timer_init(A_WAIT_BCON, otgd, set_tmout, TA_WAIT_BCON, &fsm->a_wait_bcon_tmout);
+	otg_timer_init(A_AIDL_BDIS, otgd, set_tmout, TA_AIDL_BDIS, &fsm->a_aidl_bdis_tmout);
+	otg_timer_init(A_BIDL_ADIS, otgd, set_tmout, TA_BIDL_ADIS, &fsm->a_bidl_adis_tmout);
+	otg_timer_init(B_ASE0_BRST, otgd, set_tmout, TB_ASE0_BRST, &fsm->b_ase0_brst_tmout);
+
+	otg_timer_init(B_SE0_SRP, otgd, set_tmout, TB_SE0_SRP, &fsm->b_se0_srp);
+	otg_timer_init(B_SRP_FAIL, otgd, set_tmout, TB_SRP_FAIL, &fsm->b_srp_done);
+
+	otg_timer_init(A_WAIT_ENUM, otgd, set_tmout, TB_SRP_FAIL, NULL);
+}
+
+/**
+ * OTG FSM ops function to add timer
+ */
+static void usb_otg_add_timer(struct otg_fsm *fsm, enum otg_fsm_timer id)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+	struct otg_timer *otgtimer = &otgd->timers[id];
+	struct hrtimer *timer = &otgtimer->timer;
+
+	if (!otgd->fsm_running)
+		return;
+
+	/* if timer is already active, exit */
+	if (hrtimer_active(timer)) {
+		dev_err(otgd->dev, "otg: timer %d is already running\n", id);
+		return;
+	}
+
+	hrtimer_start(timer, otgtimer->timeout, HRTIMER_MODE_REL);
+}
+
+/**
+ * OTG FSM ops function to delete timer
+ */
+static void usb_otg_del_timer(struct otg_fsm *fsm, enum otg_fsm_timer id)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+	struct hrtimer *timer = &otgd->timers[id].timer;
+
+	hrtimer_cancel(timer);
+}
+
+/**
+ * OTG FSM ops function to start/stop host
+ */
+static int usb_otg_start_host(struct otg_fsm *fsm, int on)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+
+	dev_dbg(otgd->dev, "otg: %s %d\n", __func__, on);
+	if (!fsm->otg->host) {
+		WARN_ONCE(1, "otg: fsm running without host\n");
+		return 0;
+	}
+
+	if (on) {
+		/* OTG device operations */
+		if (otgd->start_host)
+			otgd->start_host(fsm, on);
+
+		/* start host */
+		usb_add_hcd(otgd->primary_hcd.hcd, otgd->primary_hcd.irqnum,
+			    otgd->primary_hcd.irqflags);
+		if (otgd->shared_hcd.hcd) {
+			usb_add_hcd(otgd->shared_hcd.hcd,
+				    otgd->shared_hcd.irqnum,
+				    otgd->shared_hcd.irqflags);
+		}
+	} else {
+		/* stop host */
+		if (otgd->shared_hcd.hcd)
+			usb_remove_hcd(otgd->shared_hcd.hcd);
+		usb_remove_hcd(otgd->primary_hcd.hcd);
+
+		/* OTG device operations */
+		if (otgd->start_host)
+			otgd->start_host(fsm, on);
+	}
+
+	return 0;
+}
+
+/**
+ * OTG FSM ops function to start/stop gadget
+ */
+static int usb_otg_start_gadget(struct otg_fsm *fsm, int on)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+	struct usb_gadget *gadget = fsm->otg->gadget;
+
+	dev_dbg(otgd->dev, "otg: %s %d\n", __func__, on);
+	if (!gadget) {
+		WARN_ONCE(1, "otg: fsm running without gadget\n");
+		return 0;
+	}
+
+	if (on) {
+		/* OTG device operations */
+		if (otgd->start_gadget)
+			otgd->start_gadget(fsm, on);
+
+		usb_gadget_start(fsm->otg->gadget);
+	} else {
+		usb_gadget_stop(fsm->otg->gadget);
+
+		/* OTG device operations */
+		if (otgd->start_gadget)
+			otgd->start_gadget(fsm, on);
+
+	}
+
+	return 0;
+}
+
+/**
+ * OTG FSM work function
+ */
+static void usb_otg_work(struct work_struct *work)
+{
+	struct otg_data *otgd = container_of(work, struct otg_data, work);
+
+	if (otg_statemachine(&otgd->fsm)) {
+		/* state changed. any action ? */
+	}
+}
+
+/**
+ * usb_otg_register() - Register the OTG device to OTG core
+ * @parent_device:	parent device of Host & Gadget controllers.
+ * @otg_fsm_ops:	otg state machine ops.
+ *
+ * Register parent device that contains both HCD and GCD into
+ * the USB OTG core. HCD and GCD will be prevented from starting
+ * till both are available for use.
+ *
+ * Return: struct otg_fsm * if success, NULL if error.
+ */
+struct otg_fsm *usb_otg_register(struct device *parent_dev,
+				 struct otg_fsm_ops *fsm_ops)
+{
+	struct otg_data *otgd;
+	int ret = 0;
+
+	if (!parent_dev || !fsm_ops)
+		return ERR_PTR(-EINVAL);
+
+	/* already in list? */
+	mutex_lock(&otg_list_mutex);
+	if (usb_otg_device_get_otgd(parent_dev)) {
+		dev_err(parent_dev, "otg: %s: device already in otg list\n",
+			__func__);
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	/* allocate and add to list */
+	otgd = kzalloc(sizeof(*otgd), GFP_KERNEL);
+	if (!otgd) {
+		ret = -ENOMEM;
+		goto unlock;
+	}
+
+	otgd->dev = parent_dev;
+	INIT_WORK(&otgd->work, usb_otg_work);
+	otgd->wq = create_singlethread_workqueue("usb_otg");
+	if (!otgd->wq) {
+		dev_err(parent_dev, "otg: %s: can't create workqueue\n",
+			__func__);
+		ret = -ENODEV;
+		goto err_wq;
+	}
+
+	usb_otg_init_timers(otgd);
+
+	/* save original start host/gadget ops */
+	otgd->start_host = fsm_ops->start_host;
+	otgd->start_gadget = fsm_ops->start_gadget;
+	/* create copy of original ops */
+	otgd->fsm_ops = *fsm_ops;
+	/* override ops */
+	otgd->fsm_ops.start_host = usb_otg_start_host;
+	otgd->fsm_ops.start_gadget = usb_otg_start_gadget;
+	/* FIXME: we ignore caller's timer ops */
+	otgd->fsm_ops.add_timer = usb_otg_add_timer;
+	otgd->fsm_ops.del_timer = usb_otg_del_timer;
+	/* set otg ops */
+	otgd->fsm.ops = &otgd->fsm_ops;
+	otgd->fsm.otg = &otgd->otg;
+
+	mutex_init(&otgd->fsm.lock);
+
+	list_add_tail(&otgd->list, &otg_list);
+	mutex_unlock(&otg_list_mutex);
+	return &otgd->fsm;
+
+err_wq:
+	kfree(otgd);
+unlock:
+	mutex_unlock(&otg_list_mutex);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(usb_otg_register);
+
+/**
+ * usb_otg_unregister() - Unregister the OTG device from USB OTG core
+ * @parent_device:	parent device of Host & Gadget controllers.
+ *
+ * Unregister parent OTG deviced from USB OTG core.
+ * Prevents unregistering till both Host and Gadget controllers
+ * have unregistered from the OTG core.
+ *
+ * Return: 0 on success, error value otherwise.
+ */
+int usb_otg_unregister(struct device *parent_dev)
+{
+	struct otg_data *otgd;
+
+	mutex_lock(&otg_list_mutex);
+	otgd = usb_otg_device_get_otgd(parent_dev);
+	if (!otgd) {
+		dev_err(parent_dev, "otg: %s: device not in otg list\n",
+			__func__);
+		mutex_unlock(&otg_list_mutex);
+		return -EINVAL;
+	}
+
+	/* prevent unregister till both host & gadget have unregistered */
+	if (otgd->fsm.otg->host || otgd->fsm.otg->gadget) {
+		dev_err(parent_dev, "otg: %s: host/gadget still registered\n",
+			__func__);
+		return -EBUSY;
+	}
+
+	/* OTG FSM is halted when host/gadget unregistered */
+	destroy_workqueue(otgd->wq);
+
+	/* remove from otg list */
+	list_del(&otgd->list);
+	kfree(otgd);
+	mutex_unlock(&otg_list_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_otg_unregister);
+
+/**
+ * start/kick the OTG FSM if we can
+ * fsm->lock must be held
+ */
+static void usb_otg_start_fsm(struct otg_fsm *fsm)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+
+	if (otgd->fsm_running)
+		goto kick_fsm;
+
+	if (!fsm->otg->host) {
+		dev_info(otgd->dev, "otg: can't start till host registers\n");
+		return;
+	}
+
+	if (!fsm->otg->gadget) {
+		dev_info(otgd->dev, "otg: can't start till gadget registers\n");
+		return;
+	}
+
+	otgd->fsm_running = true;
+kick_fsm:
+	queue_work(otgd->wq, &otgd->work);
+}
+
+/**
+ * stop the OTG FSM. Stops Host & Gadget controllers as well.
+ * fsm->lock must be held
+ */
+static void usb_otg_stop_fsm(struct otg_fsm *fsm)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+	int i;
+
+	if (!otgd->fsm_running)
+		return;
+
+	/* no more new events queued */
+	otgd->fsm_running = false;
+
+	/* Stop state machine / timers */
+	for (i = 0; i < ARRAY_SIZE(otgd->timers); i++)
+		hrtimer_cancel(&otgd->timers[i].timer);
+
+	flush_workqueue(otgd->wq);
+	fsm->otg->state = OTG_STATE_UNDEFINED;
+
+	/* stop host/gadget immediately */
+	if (fsm->protocol == PROTO_HOST)
+		otg_start_host(fsm, 0);
+	else if (fsm->protocol == PROTO_GADGET)
+		otg_start_gadget(fsm, 0);
+	fsm->protocol = PROTO_UNDEF;
+}
+
+/**
+ * usb_otg_sync_inputs - Sync OTG inputs with the OTG state machine
+ * @fsm:	OTG FSM instance
+ *
+ * Used by the OTG driver to update the inputs to the OTG
+ * state machine.
+ *
+ * Can be called in IRQ context.
+ */
+void usb_otg_sync_inputs(struct otg_fsm *fsm)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+
+	/* Don't kick FSM till it has started */
+	if (!otgd->fsm_running)
+		return;
+
+	/* Kick FSM */
+	queue_work(otgd->wq, &otgd->work);
+}
+EXPORT_SYMBOL_GPL(usb_otg_sync_inputs);
+
+/**
+ * usb_otg_kick_fsm - Kick the OTG state machine
+ * @hcd_gcd_device:	Host/Gadget controller device
+ *
+ * Used by USB host/device stack to sync OTG related
+ * events to the OTG state machine.
+ * e.g. change in host_bus->b_hnp_enable, gadget->b_hnp_enable
+ *
+ * Returns: 0 on success, error value otherwise.
+ */
+int usb_otg_kick_fsm(struct device *hcd_gcd_device)
+{
+	struct otg_data *otgd;
+
+	mutex_lock(&otg_list_mutex);
+	otgd = usb_otg_device_get_otgd(hcd_gcd_device->parent);
+	if (!otgd) {
+		dev_err(hcd_gcd_device, "otg: %s: invalid host/gadget device\n",
+			__func__);
+		mutex_unlock(&otg_list_mutex);
+		return -ENODEV;
+	}
+
+	mutex_unlock(&otg_list_mutex);
+	usb_otg_sync_inputs(&otgd->fsm);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_otg_kick_fsm);
+
+/**
+ * usb_otg_register_hcd - Register Host controller to OTG core
+ * @hcd:	Host controller device
+ *
+ * This is used by the USB Host stack to register the Host controller
+ * to the OTG core. Host controller must not be started by the
+ * caller as it is left upto the OTG state machine to do so.
+ *
+ * Returns: 0 on success, error value otherwise.
+ */
+int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
+			 unsigned long irqflags)
+{
+	struct otg_data *otgd;
+	struct device *otg_dev = hcd->self.controller->parent;
+
+	mutex_lock(&otg_list_mutex);
+	otgd = usb_otg_device_get_otgd(otg_dev);
+	if (!otgd) {
+		dev_dbg(otg_dev, "otg: %s: device not registered to otg core\n",
+			__func__);
+		mutex_unlock(&otg_list_mutex);
+		return -EINVAL;
+	}
+
+	mutex_unlock(&otg_list_mutex);
+	/* HCD will be started by OTG fsm when needed */
+	mutex_lock(&otgd->fsm.lock);
+	if (otgd->primary_hcd.hcd) {
+		/* probably a shared HCD ? */
+		if (usb_hcd_is_primary_hcd(hcd)) {
+			dev_err(otg_dev, "otg: primary host already registered\n");
+			goto err;
+		}
+
+		if (hcd->shared_hcd == otgd->primary_hcd.hcd) {
+			if (otgd->shared_hcd.hcd) {
+				dev_err(otg_dev, "otg: shared host already registered\n");
+				goto err;
+			}
+
+			otgd->shared_hcd.hcd = hcd;
+			otgd->shared_hcd.irqnum = irqnum;
+			otgd->shared_hcd.irqflags = irqflags;
+			dev_info(otg_dev, "otg: shared host %s registered\n",
+				 dev_name(hcd->self.controller));
+		} else {
+			dev_err(otg_dev, "otg: invalid shared host %s\n",
+				dev_name(hcd->self.controller));
+			goto err;
+		}
+	} else {
+		if (!usb_hcd_is_primary_hcd(hcd)) {
+			dev_err(otg_dev, "otg: primary host must be registered first\n");
+			goto err;
+		}
+
+		otgd->primary_hcd.hcd = hcd;
+		otgd->primary_hcd.irqnum = irqnum;
+		otgd->primary_hcd.irqflags = irqflags;
+		dev_info(otg_dev, "otg: primary host %s registered\n",
+			 dev_name(hcd->self.controller));
+
+	}
+
+	/*
+	 * we're ready only if we have shared HCD
+	 * or we don't need shared HCD.
+	 */
+	if (otgd->shared_hcd.hcd || !otgd->primary_hcd.hcd->shared_hcd) {
+		otgd->fsm.otg->host = hcd_to_bus(hcd);
+		/* FIXME: set bus->otg_port if this is true OTG port with HNP */
+
+		/* start FSM */
+		usb_otg_start_fsm(&otgd->fsm);
+	} else {
+		dev_dbg(otg_dev, "otg: can't start till shared host registers\n");
+	}
+
+	mutex_unlock(&otgd->fsm.lock);
+
+	return 0;
+
+err:
+	mutex_unlock(&otgd->fsm.lock);
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(usb_otg_register_hcd);
+
+/**
+ * usb_otg_unregister_hcd - Unregister Host controller from OTG core
+ * @hcd:	Host controller device
+ *
+ * This is used by the USB Host stack to unregister the Host controller
+ * from the OTG core. Ensures that Host controller is not running
+ * on successful return.
+ *
+ * Returns: 0 on success, error value otherwise.
+ */
+int usb_otg_unregister_hcd(struct usb_hcd *hcd)
+{
+	struct otg_data *otgd;
+	struct usb_bus *bus = hcd_to_bus(hcd);
+	struct device *otg_dev = bus->controller->parent;
+
+	mutex_lock(&otg_list_mutex);
+	otgd = usb_otg_device_get_otgd(otg_dev);
+	if (!otgd) {
+		dev_err(otg_dev, "otg: %s: device not registered to otg core\n",
+			__func__);
+		mutex_unlock(&otg_list_mutex);
+		return -EINVAL;
+	}
+
+	mutex_unlock(&otg_list_mutex);
+
+	mutex_lock(&otgd->fsm.lock);
+	if (hcd == otgd->primary_hcd.hcd) {
+		otgd->primary_hcd.hcd = NULL;
+		dev_info(otg_dev, "otg: primary host %s unregistered\n",
+			 dev_name(bus->controller));
+	} else if (hcd == otgd->shared_hcd.hcd) {
+		otgd->shared_hcd.hcd = NULL;
+		dev_info(otg_dev, "otg: shared host %s unregistered\n",
+			 dev_name(bus->controller));
+	} else {
+		dev_err(otg_dev, "otg: host %s wasn't registered with otg\n",
+			dev_name(bus->controller));
+		mutex_unlock(&otgd->fsm.lock);
+		return -EINVAL;
+	}
+
+	/* stop FSM & Host */
+	usb_otg_stop_fsm(&otgd->fsm);
+	otgd->fsm.otg->host = NULL;
+
+	mutex_unlock(&otgd->fsm.lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_otg_unregister_hcd);
+
+/**
+ * usb_otg_register_gadget - Register Gadget controller to OTG core
+ * @gadget:	Gadget controller
+ *
+ * This is used by the USB Gadget stack to register the Gadget controller
+ * to the OTG core. Gadget controller must not be started by the
+ * caller as it is left upto the OTG state machine to do so.
+ *
+ * Gadget core must call this only when all resources required for
+ * gadget controller to run are available.
+ * i.e. gadget function driver is available.
+ *
+ * Returns: 0 on success, error value otherwise.
+ */
+int usb_otg_register_gadget(struct usb_gadget *gadget)
+{
+	struct otg_data *otgd;
+	struct device *otg_dev = gadget->dev.parent;
+
+	mutex_lock(&otg_list_mutex);
+	otgd = usb_otg_device_get_otgd(otg_dev);
+	if (!otgd) {
+		dev_err(otg_dev, "otg: %s: device not registered to otg core\n",
+			__func__);
+		mutex_unlock(&otg_list_mutex);
+		return -EINVAL;
+	}
+
+	mutex_unlock(&otg_list_mutex);
+
+	mutex_lock(&otgd->fsm.lock);
+	if (otgd->fsm.otg->gadget) {
+		dev_err(otg_dev, "otg: gadget already registered with otg\n");
+		mutex_unlock(&otgd->fsm.lock);
+		return -EINVAL;
+	}
+
+	otgd->fsm.otg->gadget = gadget;
+	dev_info(otg_dev, "otg: gadget %s registered\n",
+		 dev_name(&gadget->dev));
+
+	/* start FSM */
+	usb_otg_start_fsm(&otgd->fsm);
+	mutex_unlock(&otgd->fsm.lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_otg_register_gadget);
+
+/**
+ * usb_otg_unregister_gadget - Unregister Gadget controller from OTG core
+ * @gadget:	Gadget controller
+ *
+ * This is used by the USB Gadget stack to unregister the Gadget controller
+ * from the OTG core. Ensures that Gadget controller is not running
+ * on successful return.
+ *
+ * Returns: 0 on success, error value otherwise.
+ */
+int usb_otg_unregister_gadget(struct usb_gadget *gadget)
+{
+	struct otg_data *otgd;
+	struct device *otg_dev = gadget->dev.parent;
+
+	mutex_lock(&otg_list_mutex);
+	otgd = usb_otg_device_get_otgd(otg_dev);
+	if (!otgd) {
+		dev_err(otg_dev, "otg: %s: device not registered to otg core\n",
+			__func__);
+		mutex_unlock(&otg_list_mutex);
+		return -EINVAL;
+	}
+
+	mutex_unlock(&otg_list_mutex);
+
+	mutex_lock(&otgd->fsm.lock);
+	if (otgd->fsm.otg->gadget != gadget) {
+		dev_err(otg_dev, "otg: gadget %s wasn't registered with otg\n",
+			dev_name(&gadget->dev));
+		mutex_unlock(&otgd->fsm.lock);
+		return -EINVAL;
+	}
+
+	/* Stop FSM & gadget */
+	usb_otg_stop_fsm(&otgd->fsm);
+	otgd->fsm.otg->gadget = NULL;
+	mutex_unlock(&otgd->fsm.lock);
+
+	dev_info(otg_dev, "otg: gadget %s unregistered\n",
+		 dev_name(&gadget->dev));
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_otg_unregister_gadget);
+
+/**
+ * usb_otg_fsm_to_dev - Get OTG controller device from struct otg_fsm
+ * @fsm:	otg_fsm data structure
+ *
+ * This is used by the OTG controller driver to get it's device node
+ * from any of the otg_fsm->ops.
+ */
+struct device *usb_otg_fsm_to_dev(struct otg_fsm *fsm)
+{
+	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
+
+	return otgd->dev;
+}
+EXPORT_SYMBOL_GPL(usb_otg_fsm_to_dev);
diff --git a/drivers/usb/common/usb-otg.h b/drivers/usb/common/usb-otg.h
new file mode 100644
index 0000000..05331f0
--- /dev/null
+++ b/drivers/usb/common/usb-otg.h
@@ -0,0 +1,71 @@
+/**
+ * drivers/usb/common/usb-otg.h - USB OTG core local header
+ *
+ * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com
+ * Author: Roger Quadros <rogerq@xxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef __DRIVERS_USB_COMMON_USB_OTG_H
+#define __DRIVERS_USB_COMMON_USB_OTG_H
+
+/*
+ *  A-DEVICE timing constants
+ */
+
+/* Wait for VBUS Rise  */
+#define TA_WAIT_VRISE        (100)	/* a_wait_vrise: section 7.1.2
+					 * a_wait_vrise_tmr: section 7.4.5.1
+					 * TA_VBUS_RISE <= 100ms, section 4.4
+					 * Table 4-1: Electrical Characteristics
+					 * ->DC Electrical Timing
+					 */
+/* Wait for VBUS Fall  */
+#define TA_WAIT_VFALL        (1000)	/* a_wait_vfall: section 7.1.7
+					 * a_wait_vfall_tmr: section: 7.4.5.2
+					 */
+/* Wait for B-Connect */
+#define TA_WAIT_BCON         (10000)	/* a_wait_bcon: section 7.1.3
+					 * TA_WAIT_BCON: should be between 1100
+					 * and 30000 ms, section 5.5, Table 5-1
+					 */
+/* A-Idle to B-Disconnect */
+#define TA_AIDL_BDIS         (5000)	/* a_suspend min 200 ms, section 5.2.1
+					 * TA_AIDL_BDIS: section 5.5, Table 5-1
+					 */
+/* B-Idle to A-Disconnect */
+#define TA_BIDL_ADIS         (500)	/* TA_BIDL_ADIS: section 5.2.1
+					 * 500ms is used for B switch to host
+					 * for safe
+					 */
+
+/*
+ * B-device timing constants
+ */
+
+/* Data-Line Pulse Time*/
+#define TB_DATA_PLS          (10)	/* b_srp_init,continue 5~10ms
+					 * section:5.1.3
+					 */
+/* SRP Fail Time  */
+#define TB_SRP_FAIL          (6000)	/* b_srp_init,fail time 5~6s
+					 * section:5.1.6
+					 */
+/* A-SE0 to B-Reset  */
+#define TB_ASE0_BRST         (155)	/* minimum 155 ms, section:5.3.1 */
+/* SE0 Time Before SRP */
+#define TB_SE0_SRP           (1000)	/* b_idle,minimum 1s, section:5.1.2 */
+/* SSEND time before SRP */
+#define TB_SSEND_SRP         (1500)	/* minimum 1.5 sec, section:5.1.2 */
+
+#define TB_SESS_VLD          (1000)
+
+#endif /* __DRIVERS_USB_COMMON_USB_OTG_H */
diff --git a/drivers/usb/core/Kconfig b/drivers/usb/core/Kconfig
index cc0ced0..43a0d2d 100644
--- a/drivers/usb/core/Kconfig
+++ b/drivers/usb/core/Kconfig
@@ -84,3 +84,11 @@ config USB_OTG_FSM
 	  Implements OTG Finite State Machine as specified in On-The-Go
 	  and Embedded Host Supplement to the USB Revision 2.0 Specification.
 
+config USB_OTG_CORE
+	tristate "USB OTG core"
+	depends on USB
+	select USB_OTG_FSM
+	help
+	  Standardize the way OTG is implemented on Linux. The OTG state
+	  machine is instantiated here instead of being done in each controller
+	  driver.
diff --git a/include/linux/usb/usb-otg.h b/include/linux/usb/usb-otg.h
new file mode 100644
index 0000000..8987cd1
--- /dev/null
+++ b/include/linux/usb/usb-otg.h
@@ -0,0 +1,94 @@
+/**
+ * include/linux/usb/usb-otg.h - USB OTG core
+ *
+ * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com
+ * Author: Roger Quadros <rogerq@xxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef __LINUX_USB_OTG_CORE_H
+#define __LINUX_USB_OTG_CORE_H
+
+#include <linux/device.h>
+#include <linux/usb.h>
+#include <linux/usb/hcd.h>
+#include <linux/usb/gadget.h>
+#include <linux/usb/otg-fsm.h>
+
+#if IS_ENABLED(CONFIG_USB_OTG_CORE)
+struct otg_fsm *usb_otg_register(struct device *parent_dev,
+				 struct otg_fsm_ops *fsm_ops);
+int usb_otg_unregister(struct device *parent_dev);
+int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
+			 unsigned long irqflags);
+int usb_otg_unregister_hcd(struct usb_hcd *hcd);
+int usb_otg_register_gadget(struct usb_gadget *gadget);
+int usb_otg_unregister_gadget(struct usb_gadget *gadget);
+void usb_otg_sync_inputs(struct otg_fsm *fsm);
+int usb_otg_kick_fsm(struct device *hcd_gcd_device);
+bool usb_otg_gadget_can_start(struct usb_gadget *gadget);
+struct device *usb_otg_fsm_to_dev(struct otg_fsm *fsm);
+
+#else /* CONFIG_USB_OTG_CORE */
+
+static inline struct otg_fsm *usb_otg_register(struct device *parent_dev,
+					       struct otg_fsm_ops *fsm_ops)
+{
+	return ERR_PTR(-ENOSYS);
+}
+
+static inline int usb_otg_unregister(struct device *parent_dev)
+{
+	return -ENOSYS;
+}
+
+static inline int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
+				       unsigned long irqflags)
+{
+	return -ENOSYS;
+}
+
+int usb_otg_unregister_hcd(struct usb_hcd *hcd)
+{
+	return -ENOSYS;
+}
+
+static inline int usb_otg_register_gadget(struct usb_gadget *gadget)
+{
+	return -ENOSYS;
+}
+
+static inline int usb_otg_unregister_gadget(struct usb_gadget *gadget)
+{
+	return -ENOSYS;
+}
+
+static inline void usb_otg_sync_inputs(struct otg_fsm *fsm)
+{
+}
+
+int usb_otg_kick_fsm(struct device *hcd_gcd_device)
+{
+	return -ENOSYS;
+}
+
+bool usb_otg_gadget_can_start(struct usb_gadget *gadget)
+{
+	return true;
+}
+
+static inline struct device *usb_otg_fsm_to_dev(struct otg_fsm *fsm)
+{
+	return NULL;
+}
+#endif /* CONFIG_USB_OTG_CORE */
+
+#endif /* __LINUX_USB_OTG_CORE */
-- 
2.1.0

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