[PATCH 3/7] usb: misc: add common code for Intel dual role port mux

[Lu Baolu]

Several Intel PCHs and SOCs have an internal mux that is used to
share one USB port between device controller and host controller.

A usb port mux could be abstracted as the following elements:
1) mux state: HOST or PERIPHERAL;
2) an extcon cable which triggers the change of mux state between
   HOST and PERIPHERAL;
3) The required action to do the real port switch.

This patch adds the common code to handle usb port mux. With this
common code, the individual mux driver, which always is platform
dependent, could focus on the real operation of mux switch.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Reviewed-by: Felipe Balbi <balbi@xxxxxxxxxx>
---
 MAINTAINERS               |   7 ++
 drivers/usb/misc/Kconfig  |   4 ++
 drivers/usb/misc/Makefile |   2 +
 drivers/usb/misc/mux.c    | 172 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/usb/mux.h   |  71 +++++++++++++++++++
 5 files changed, 256 insertions(+)
 create mode 100644 drivers/usb/misc/mux.c
 create mode 100644 include/linux/usb/mux.h

diff --git a/MAINTAINERS b/MAINTAINERS
index d894ee2..45f1e1e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11389,6 +11389,13 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git
 S:	Maintained
 F:	drivers/usb/phy/
 
+USB PORT MUX DRIVER
+M:	Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
+L:	linux-usb@xxxxxxxxxxxxxxx
+S:	Supported
+F:	drivers/usb/misc/mux.c
+F:	include/linux/usb/mux.h
+
 USB PRINTER DRIVER (usblp)
 M:	Pete Zaitcev <zaitcev@xxxxxxxxxx>
 L:	linux-usb@xxxxxxxxxxxxxxx
diff --git a/drivers/usb/misc/Kconfig b/drivers/usb/misc/Kconfig
index f7a7fc2..6496d17 100644
--- a/drivers/usb/misc/Kconfig
+++ b/drivers/usb/misc/Kconfig
@@ -3,6 +3,10 @@
 #
 comment "USB Miscellaneous drivers"
 
+config USB_MUX
+	select EXTCON
+	def_bool n
+
 config USB_EMI62
 	tristate "EMI 6|2m USB Audio interface support"
 	---help---
diff --git a/drivers/usb/misc/Makefile b/drivers/usb/misc/Makefile
index 45fd4ac..fd79dd5 100644
--- a/drivers/usb/misc/Makefile
+++ b/drivers/usb/misc/Makefile
@@ -29,3 +29,5 @@ obj-$(CONFIG_USB_CHAOSKEY)		+= chaoskey.o
 
 obj-$(CONFIG_USB_SISUSBVGA)		+= sisusbvga/
 obj-$(CONFIG_USB_LINK_LAYER_TEST)	+= lvstest.o
+
+obj-$(CONFIG_USB_MUX)			+= mux.o
diff --git a/drivers/usb/misc/mux.c b/drivers/usb/misc/mux.c
new file mode 100644
index 0000000..e353fff
--- /dev/null
+++ b/drivers/usb/misc/mux.c
@@ -0,0 +1,172 @@
+/**
+ * mux.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/notifier.h>
+#include <linux/usb/mux.h>
+#include <linux/debugfs.h>
+#include <linux/err.h>
+
+static int usb_mux_change_state(struct usb_mux *mux, int state)
+{
+	int ret;
+	struct usb_mux_dev *umdev = mux->umdev;
+
+	dev_WARN_ONCE(umdev->dev, !mutex_is_locked(&mux->mux_mutex),
+			"mutex is unlocked\n");
+
+	mux->mux_state = state;
+
+	if (mux->mux_state)
+		ret = umdev->cable_set_cb(umdev);
+	else
+		ret = umdev->cable_unset_cb(umdev);
+
+	return ret;
+}
+
+static int usb_mux_notifier(struct notifier_block *nb,
+		unsigned long event, void *ptr)
+{
+	struct usb_mux *mux;
+	int state;
+	int ret = NOTIFY_DONE;
+
+	mux = container_of(nb, struct usb_mux, nb);
+
+	state = extcon_get_cable_state(mux->obj.edev,
+			mux->umdev->cable_name);
+
+	if (mux->mux_state == -1 || mux->mux_state != state) {
+		mutex_lock(&mux->mux_mutex);
+		ret = usb_mux_change_state(mux, state);
+		mutex_unlock(&mux->mux_mutex);
+	}
+
+	return ret;
+}
+
+static ssize_t mux_debug_read(struct file *file, char __user *user_buf,
+		size_t len, loff_t *offset)
+{
+	struct usb_mux *mux = file->private_data;
+	char output_buf[16];
+
+	memset(output_buf, 0, sizeof(output_buf));
+	if (mux->mux_state)
+		strcpy(output_buf, "host\n");
+	else
+		strcpy(output_buf, "peripheral\n");
+
+	return simple_read_from_buffer(user_buf, len, offset,
+			output_buf, strlen(output_buf));
+}
+
+static ssize_t mux_debug_write(struct file *file, const char __user *user_buf,
+		size_t count, loff_t *offset)
+{
+	struct usb_mux *mux = file->private_data;
+	char input_buf[16];
+	int size, state;
+
+	size = min(count, sizeof(input_buf) - 1);
+	memset(input_buf, 0, sizeof(input_buf));
+	if (strncpy_from_user(input_buf, user_buf, size) < 0)
+		return -EFAULT;
+
+	if (!strncmp(input_buf, "host", 4))
+		state = 1;
+	else if (!strncmp(input_buf, "peripheral", 10))
+		state = 0;
+	else
+		state = -1;
+
+	if (state != -1) {
+		mutex_lock(&mux->mux_mutex);
+		usb_mux_change_state(mux, state);
+		mutex_unlock(&mux->mux_mutex);
+	}
+
+	return count;
+}
+
+static const struct file_operations mux_debug_fops = {
+	.read =		mux_debug_read,
+	.write =	mux_debug_write,
+	.open =		simple_open,
+	.llseek =	default_llseek,
+};
+
+int usb_mux_register(struct usb_mux_dev *umdev)
+{
+	int ret;
+	struct device *dev = umdev->dev;
+	struct usb_mux *mux;
+
+	if (!umdev->cable_name)
+		return -ENODEV;
+
+	mux = devm_kzalloc(dev, sizeof(*mux), GFP_KERNEL);
+	if (!mux)
+		return -ENOMEM;
+
+	mux->umdev = umdev;
+	mux->nb.notifier_call = usb_mux_notifier;
+	mutex_init(&mux->mux_mutex);
+	mux->mux_state = -1;
+	dev_set_drvdata(dev, mux);
+
+	ret = extcon_register_interest(&mux->obj, umdev->extcon_name,
+			umdev->cable_name, &mux->nb);
+	if (ret) {
+		dev_err(dev, "failed to register extcon notifier\n");
+		return -ENODEV;
+	}
+
+	usb_mux_notifier(&mux->nb, 0, NULL);
+
+	mux->debug_file = debugfs_create_file("usb_mux", 0600,
+			usb_debug_root, mux, &mux_debug_fops);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_mux_register);
+
+int usb_mux_unregister(struct device *dev)
+{
+	struct usb_mux *mux = dev_get_drvdata(dev);
+
+	debugfs_remove(mux->debug_file);
+	extcon_unregister_interest(&mux->obj);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_mux_unregister);
+
+struct usb_mux_dev *usb_mux_get_dev(struct device *dev)
+{
+	struct usb_mux *mux = dev_get_drvdata(dev);
+
+	if (mux)
+		return mux->umdev;
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(usb_mux_get_dev);
+
+#ifdef CONFIG_PM_SLEEP
+void usb_mux_complete(struct device *dev)
+{
+	struct usb_mux *mux = dev_get_drvdata(dev);
+
+	usb_mux_notifier(&mux->nb, 0, NULL);
+}
+EXPORT_SYMBOL_GPL(usb_mux_complete);
+#endif
diff --git a/include/linux/usb/mux.h b/include/linux/usb/mux.h
new file mode 100644
index 0000000..5dada48
--- /dev/null
+++ b/include/linux/usb/mux.h
@@ -0,0 +1,71 @@
+/**
+ * mux.h - USB Port Mux defines
+ *
+ * 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_MUX_H
+#define __LINUX_USB_MUX_H
+
+#include <linux/extcon.h>
+#include <linux/usb.h>
+
+struct usb_mux_dev {
+	struct device	*dev;
+	char		*extcon_name;
+	char		*cable_name;
+	int		(*cable_set_cb)(struct usb_mux_dev *mux);
+	int		(*cable_unset_cb)(struct usb_mux_dev *mux);
+};
+
+struct usb_mux {
+	struct usb_mux_dev		*umdev;
+	struct notifier_block		nb;
+	struct extcon_specific_cable_nb	obj;
+
+	/*
+	 * The state of the mux.
+	 * 0, 1 - mux switch state
+	 * -1   - uninitialized state
+	 *
+	 * mux_mutex is lock to protect mux_state
+	 */
+	int				mux_state;
+	struct mutex			mux_mutex;
+
+	struct dentry			*debug_file;
+};
+
+#if IS_ENABLED(CONFIG_USB_MUX)
+extern int usb_mux_register(struct usb_mux_dev *mux);
+extern int usb_mux_unregister(struct device *dev);
+extern struct usb_mux_dev *usb_mux_get_dev(struct device *dev);
+
+#ifdef CONFIG_PM_SLEEP
+extern void usb_mux_complete(struct device *dev);
+#endif
+
+#else /* CONFIG_USB_MUX */
+static inline int usb_mux_register(struct usb_mux_dev *mux)
+{
+	return -ENODEV;
+}
+
+static inline int usb_mux_unregister(struct device *dev)
+{
+	return 0;
+}
+
+static inline struct usb_mux_dev *usb_mux_get_dev(struct device *dev)
+{
+	return NULL;
+}
+#endif /* CONFIG_USB_MUX */
+
+#endif /* __LINUX_USB_MUX_H */
-- 
2.1.4