[PATCH v9 2/7] usb: mux: add generic code for dual role port mux

[Lu Baolu]

Several Intel platforms implement USB dual role by having completely
separate xHCI and dwc3 IPs in PCH or SOC silicons. These two IPs share
a single USB port. There is another external port mux which controls
where the data lines should go. While the USB controllers are part of
the silicon, the port mux design are platform specific.

This patch adds the generic code to handle such multiple roles of a
usb port. It exports the necessary interfaces for other components to
register or unregister a usb mux device, and to control its role.
It registers the mux device with sysfs as well, so that users are able
to control the port role from user space.

Some other archs (e.g. Renesas R-Car gen2 SoCs) need an external mux to
swap usb roles as well. This code could also be leveraged for those archs.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Reviewed-by: Felipe Balbi <balbi@xxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-bus-platform |  18 +++
 drivers/usb/Kconfig                          |   2 +
 drivers/usb/Makefile                         |   1 +
 drivers/usb/mux/Kconfig                      |   8 ++
 drivers/usb/mux/Makefile                     |   4 +
 drivers/usb/mux/portmux-core.c               | 202 +++++++++++++++++++++++++++
 include/linux/usb/portmux.h                  |  90 ++++++++++++
 7 files changed, 325 insertions(+)
 create mode 100644 drivers/usb/mux/Kconfig
 create mode 100644 drivers/usb/mux/Makefile
 create mode 100644 drivers/usb/mux/portmux-core.c
 create mode 100644 include/linux/usb/portmux.h

diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
index 5172a61..b994e4e 100644
--- a/Documentation/ABI/testing/sysfs-bus-platform
+++ b/Documentation/ABI/testing/sysfs-bus-platform
@@ -18,3 +18,21 @@ Description:
 		devices to opt-out of driver binding using a driver_override
 		name such as "none".  Only a single driver may be specified in
 		the override, there is no support for parsing delimiters.
+
+What:		/sys/bus/platform/devices/.../portmux.N/name
+		/sys/bus/platform/devices/.../portmux.N/state
+Date:		April 2016
+Contact:	Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
+Description:
+		In some platforms, a single USB port is shared between a USB host
+		controller and a device controller. A USB mux driver is needed to
+		handle the port mux. Read-only attribute "name" shows the name of
+		the port mux device. "state" attribute shows and stores the mux
+		state.
+		For read:
+		'unknown'    - the mux hasn't been set yet;
+		'peripheral' - mux has been switched to PERIPHERAL controller;
+		'host'       - mux has been switched to HOST controller.
+		For write:
+		'peripheral' - mux will be switched to PERIPHERAL controller;
+		'host'       - mux will be switched to HOST controller.
diff --git a/drivers/usb/Kconfig b/drivers/usb/Kconfig
index 8689dcb..328916e 100644
--- a/drivers/usb/Kconfig
+++ b/drivers/usb/Kconfig
@@ -148,6 +148,8 @@ endif # USB
 
 source "drivers/usb/phy/Kconfig"
 
+source "drivers/usb/mux/Kconfig"
+
 source "drivers/usb/gadget/Kconfig"
 
 config USB_LED_TRIG
diff --git a/drivers/usb/Makefile b/drivers/usb/Makefile
index dca7856..9a92338 100644
--- a/drivers/usb/Makefile
+++ b/drivers/usb/Makefile
@@ -6,6 +6,7 @@
 
 obj-$(CONFIG_USB)		+= core/
 obj-$(CONFIG_USB_SUPPORT)	+= phy/
+obj-$(CONFIG_USB_SUPPORT)	+= mux/
 
 obj-$(CONFIG_USB_DWC3)		+= dwc3/
 obj-$(CONFIG_USB_DWC2)		+= dwc2/
diff --git a/drivers/usb/mux/Kconfig b/drivers/usb/mux/Kconfig
new file mode 100644
index 0000000..ba778f2
--- /dev/null
+++ b/drivers/usb/mux/Kconfig
@@ -0,0 +1,8 @@
+#
+# USB port mux driver configuration
+#
+
+menuconfig USB_PORTMUX
+	bool "USB dual role port MUX support"
+	help
+	  Generic USB dual role port mux support.
diff --git a/drivers/usb/mux/Makefile b/drivers/usb/mux/Makefile
new file mode 100644
index 0000000..f85df92
--- /dev/null
+++ b/drivers/usb/mux/Makefile
@@ -0,0 +1,4 @@
+#
+# Makefile for USB port mux drivers
+#
+obj-$(CONFIG_USB_PORTMUX)		+= portmux-core.o
diff --git a/drivers/usb/mux/portmux-core.c b/drivers/usb/mux/portmux-core.c
new file mode 100644
index 0000000..75fbb45
--- /dev/null
+++ b/drivers/usb/mux/portmux-core.c
@@ -0,0 +1,202 @@
+/**
+ * portmux-core.c - USB Port Mux support
+ *
+ * Copyright (C) 2016 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
+ *
+ * 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.
+ */
+
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/usb/portmux.h>
+
+static int usb_mux_change_state(struct portmux_dev *pdev,
+				enum portmux_role role)
+{
+	struct device *dev = &pdev->dev;
+	int ret = -EINVAL;
+
+	dev_WARN_ONCE(dev,
+		      !mutex_is_locked(&pdev->mux_mutex),
+		      "mutex is unlocked\n");
+
+	switch (role) {
+	case PORTMUX_HOST:
+		if (pdev->desc->ops->set_host_cb)
+			ret = pdev->desc->ops->set_host_cb(pdev->dev.parent);
+		break;
+	case PORTMUX_DEVICE:
+		if (pdev->desc->ops->set_device_cb)
+			ret = pdev->desc->ops->set_device_cb(pdev->dev.parent);
+		break;
+	default:
+		break;
+	}
+
+	if (!ret)
+		pdev->mux_state = role;
+
+	return ret;
+}
+
+static const char * const role_name[] = {
+	"unknown",	/* PORTMUX_UNKNOWN */
+	"host",		/* PORTMUX_HOST */
+	"peripheral"	/* PORTMUX_DEVICE */
+};
+
+static ssize_t state_show(struct device *dev,
+			  struct device_attribute *attr,
+			  char *buf)
+{
+	struct portmux_dev *pdev = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", role_name[pdev->mux_state]);
+}
+
+static ssize_t state_store(struct device *dev,
+			   struct device_attribute *attr,
+			   const char *buf, size_t count)
+{
+	struct portmux_dev *pdev = dev_get_drvdata(dev);
+	enum portmux_role role;
+
+	if (sysfs_streq(buf, "peripheral"))
+		role = PORTMUX_DEVICE;
+	else if (sysfs_streq(buf, "host"))
+		role = PORTMUX_HOST;
+	else
+		return -EINVAL;
+
+	mutex_lock(&pdev->mux_mutex);
+	usb_mux_change_state(pdev, role);
+	mutex_unlock(&pdev->mux_mutex);
+
+	return count;
+}
+static DEVICE_ATTR_RW(state);
+
+static ssize_t name_show(struct device *dev,
+			 struct device_attribute *attr,
+			 char *buf)
+{
+	struct portmux_dev *pdev = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", pdev->desc->name);
+}
+static DEVICE_ATTR_RO(name);
+
+static struct attribute *portmux_attrs[] = {
+	&dev_attr_state.attr,
+	&dev_attr_name.attr,
+	NULL,
+};
+
+static struct attribute_group portmux_attr_grp = {
+	.attrs = portmux_attrs,
+};
+
+static const struct attribute_group *portmux_group[] = {
+	&portmux_attr_grp,
+	NULL,
+};
+
+static void portmux_dev_release(struct device *dev)
+{
+	dev_vdbg(dev, "%s\n", __func__);
+}
+
+/**
+ * portmux_register - register a port mux
+ * @dev: device the mux belongs to
+ * @desc: the descriptor of this port mux
+ *
+ * Called by port mux drivers to register a mux. Returns a valid
+ * pointer to struct portmux_dev on success or an ERR_PTR() on
+ * error.
+ */
+struct portmux_dev *portmux_register(struct portmux_desc *desc)
+{
+	static atomic_t portmux_no = ATOMIC_INIT(-1);
+	struct portmux_dev *pdev;
+	int ret;
+
+	/* parameter sanity check */
+	if (!desc || !desc->name || !desc->ops || !desc->dev)
+		return ERR_PTR(-EINVAL);
+
+	pdev = kzalloc(sizeof(*pdev), GFP_KERNEL);
+	if (!pdev)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_init(&pdev->mux_mutex);
+	pdev->desc = desc;
+	pdev->dev.parent = desc->dev;
+	pdev->dev.release = portmux_dev_release;
+	dev_set_name(&pdev->dev, "portmux.%lu",
+		     (unsigned long)atomic_inc_return(&portmux_no));
+	pdev->dev.groups = portmux_group;
+	ret = device_register(&pdev->dev);
+	if (ret) {
+		kfree(pdev);
+		return ERR_PTR(ret);
+	}
+
+	dev_set_drvdata(&pdev->dev, pdev);
+
+	return pdev;
+}
+EXPORT_SYMBOL_GPL(portmux_register);
+
+/**
+ * portmux_unregister - unregister a port mux
+ * @pdev: the port mux device
+ *
+ * Called by port mux drivers to release a mux.
+ */
+void portmux_unregister(struct portmux_dev *pdev)
+{
+	device_unregister(&pdev->dev);
+	kfree(pdev);
+}
+EXPORT_SYMBOL_GPL(portmux_unregister);
+
+/**
+ * portmux_switch - switch the port role
+ * @pdev: the port mux device
+ * @role: the target role
+ *
+ * Called by other components to switch the port role.
+ */
+int portmux_switch(struct portmux_dev *pdev, enum portmux_role role)
+{
+	int ret;
+
+	mutex_lock(&pdev->mux_mutex);
+	ret = usb_mux_change_state(pdev, role);
+	mutex_unlock(&pdev->mux_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(portmux_switch);
+
+#ifdef CONFIG_PM_SLEEP
+/**
+ * portmux_complete - refresh port state during system resumes back
+ * @pdev: the port mux device
+ *
+ * Called by port mux drivers to refresh port state during system
+ * resumes back.
+ */
+void portmux_complete(struct portmux_dev *pdev)
+{
+	mutex_lock(&pdev->mux_mutex);
+	usb_mux_change_state(pdev, pdev->mux_state);
+	mutex_unlock(&pdev->mux_mutex);
+}
+EXPORT_SYMBOL_GPL(portmux_complete);
+#endif
diff --git a/include/linux/usb/portmux.h b/include/linux/usb/portmux.h
new file mode 100644
index 0000000..093620a
--- /dev/null
+++ b/include/linux/usb/portmux.h
@@ -0,0 +1,90 @@
+/**
+ * portmux.h - USB Port Mux definitions
+ *
+ * Copyright (C) 2016 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
+ *
+ * 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.
+ */
+
+#ifndef __LINUX_USB_PORTMUX_H
+#define __LINUX_USB_PORTMUX_H
+
+#include <linux/device.h>
+
+/**
+ * struct portmux_ops - ops two switch the port
+ *
+ * @set_host_cb: callback for switching port to host
+ * @set_device_cb: callback for switching port to device
+ */
+struct portmux_ops {
+	int (*set_host_cb)(struct device *dev);
+	int (*set_device_cb)(struct device *dev);
+};
+
+/**
+ * struct portmux_desc - port mux device descriptor
+ *
+ * @name: the name of the mux device
+ * @dev: the parent of the mux device
+ * @ops: ops to switch the port role
+ */
+struct portmux_desc {
+	const char *name;
+	struct device *dev;
+	const struct portmux_ops *ops;
+};
+
+/**
+ * enum portmux_role - role of the port
+ */
+enum portmux_role {
+	PORTMUX_UNKNOWN,
+	PORTMUX_HOST,
+	PORTMUX_DEVICE,
+};
+
+/**
+ * struct portmux_dev - A mux device
+ *
+ * @desc: the descriptor of the mux
+ * @dev: device of this mux
+ * @mux_mutex: lock to serialize port switch operation
+ * @mux_state: state of the mux
+ */
+struct portmux_dev {
+	const struct portmux_desc *desc;
+	struct device dev;
+
+	/* lock for mux_state */
+	struct mutex mux_mutex;
+	enum portmux_role mux_state;
+};
+
+/*
+ * Functions for mux driver
+ */
+struct portmux_dev *portmux_register(struct portmux_desc *desc);
+void portmux_unregister(struct portmux_dev *pdev);
+#ifdef CONFIG_PM_SLEEP
+void portmux_complete(struct portmux_dev *pdev);
+#endif
+
+/*
+ * Functions for mux consumer
+ */
+#if defined(CONFIG_USB_PORTMUX)
+int portmux_switch(struct portmux_dev *pdev, enum portmux_role role);
+#else
+static inline int portmux_switch(struct portmux_dev *pdev,
+				 enum portmux_role role)
+{
+	return 0;
+}
+#endif
+
+#endif /* __LINUX_USB_PORTMUX_H */
-- 
2.1.4