serdev: Introduce new bus for serial attached devices

The serdev bus is designed for devices such as Bluetooth, WiFi, GPS
and NFC connected to UARTs on host processors. Tradionally these have
been handled with tty line disciplines, rfkill, and userspace glue such
as hciattach. This approach has many drawbacks since it doesn't fit
into the Linux driver model. Handling of sideband signals, power control
and firmware loading are the main issues.

This creates a serdev bus with controllers (i.e. host serial ports) and
attached devices. Typically, these are point to point connections, but
some devices have muxing protocols or a h/w mux is conceivable. Any
muxing is not yet supported with the serdev bus.
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-By: Sebastian Reichel <sre@kernel.org>
Tested-By: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -10831,6 +10831,14 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/serial/
 F:	drivers/tty/serial/
 
+SERIAL DEVICE BUS
+M:	Rob Herring <robh@kernel.org>
+L:	linux-serial@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/serial/slave-device.txt
+F:	drivers/tty/serdev/
+F:	include/linux/serdev.h
+
 SERIAL IR RECEIVER
 M:	Sean Young <sean@mess.org>
 L:	linux-media@vger.kernel.org

drivers/char/Kconfig

@@ -46,6 +46,7 @@ config SGI_MBCS
          say Y or M here, otherwise say N.
 
 source "drivers/tty/serial/Kconfig"
+source "drivers/tty/serdev/Kconfig"
 
 config TTY_PRINTK
 	tristate "TTY driver to output user messages via printk"

drivers/tty/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_R3964)		+= n_r3964.o
 obj-y				+= vt/
 obj-$(CONFIG_HVC_DRIVER)	+= hvc/
 obj-y				+= serial/
+obj-$(CONFIG_SERIAL_DEV_BUS)	+= serdev/
 
 # tty drivers
 obj-$(CONFIG_AMIGA_BUILTIN_SERIAL) += amiserial.o

drivers/tty/serdev/Kconfig

+#
+# Serial bus device driver configuration
+#
+menuconfig SERIAL_DEV_BUS
+	tristate "Serial device bus"
+	help
+	  Core support for devices connected via a serial port.
+

drivers/tty/serdev/Makefile

+serdev-objs := core.o
+
+obj-$(CONFIG_SERIAL_DEV_BUS) += serdev.o

include/linux/serdev.h

+/*
+ * Copyright (C) 2016-2017 Linaro Ltd., Rob Herring <robh@kernel.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only 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_SERDEV_H
+#define _LINUX_SERDEV_H
+
+#include <linux/types.h>
+#include <linux/device.h>
+
+struct serdev_controller;
+struct serdev_device;
+
+/*
+ * serdev device structures
+ */
+
+/**
+ * struct serdev_device_ops - Callback operations for a serdev device
+ * @receive_buf:	Function called with data received from device.
+ * @write_wakeup:	Function called when ready to transmit more data.
+ */
+struct serdev_device_ops {
+	int (*receive_buf)(struct serdev_device *, const unsigned char *, size_t);
+	void (*write_wakeup)(struct serdev_device *);
+};
+
+/**
+ * struct serdev_device - Basic representation of an serdev device
+ * @dev:	Driver model representation of the device.
+ * @nr:		Device number on serdev bus.
+ * @ctrl:	serdev controller managing this device.
+ * @ops:	Device operations.
+ */
+struct serdev_device {
+	struct device dev;
+	int nr;
+	struct serdev_controller *ctrl;
+	const struct serdev_device_ops *ops;
+};
+
+static inline struct serdev_device *to_serdev_device(struct device *d)
+{
+	return container_of(d, struct serdev_device, dev);
+}
+
+/**
+ * struct serdev_device_driver - serdev slave device driver
+ * @driver:	serdev device drivers should initialize name field of this
+ *		structure.
+ * @probe:	binds this driver to a serdev device.
+ * @remove:	unbinds this driver from the serdev device.
+ */
+struct serdev_device_driver {
+	struct device_driver driver;
+	int	(*probe)(struct serdev_device *);
+	void	(*remove)(struct serdev_device *);
+};
+
+static inline struct serdev_device_driver *to_serdev_device_driver(struct device_driver *d)
+{
+	return container_of(d, struct serdev_device_driver, driver);
+}
+
+/*
+ * serdev controller structures
+ */
+struct serdev_controller_ops {
+	int (*write_buf)(struct serdev_controller *, const unsigned char *, size_t);
+	void (*write_flush)(struct serdev_controller *);
+	int (*write_room)(struct serdev_controller *);
+	int (*open)(struct serdev_controller *);
+	void (*close)(struct serdev_controller *);
+	void (*set_flow_control)(struct serdev_controller *, bool);
+	unsigned int (*set_baudrate)(struct serdev_controller *, unsigned int);
+};
+
+/**
+ * struct serdev_controller - interface to the serdev controller
+ * @dev:	Driver model representation of the device.
+ * @nr:		number identifier for this controller/bus.
+ * @serdev:	Pointer to slave device for this controller.
+ * @ops:	Controller operations.
+ */
+struct serdev_controller {
+	struct device		dev;
+	unsigned int		nr;
+	struct serdev_device	*serdev;
+	const struct serdev_controller_ops *ops;
+};
+
+static inline struct serdev_controller *to_serdev_controller(struct device *d)
+{
+	return container_of(d, struct serdev_controller, dev);
+}
+
+static inline void *serdev_device_get_drvdata(const struct serdev_device *serdev)
+{
+	return dev_get_drvdata(&serdev->dev);
+}
+
+static inline void serdev_device_set_drvdata(struct serdev_device *serdev, void *data)
+{
+	dev_set_drvdata(&serdev->dev, data);
+}
+
+/**
+ * serdev_device_put() - decrement serdev device refcount
+ * @serdev	serdev device.
+ */
+static inline void serdev_device_put(struct serdev_device *serdev)
+{
+	if (serdev)
+		put_device(&serdev->dev);
+}
+
+static inline void serdev_device_set_client_ops(struct serdev_device *serdev,
+					      const struct serdev_device_ops *ops)
+{
+	serdev->ops = ops;
+}
+
+static inline
+void *serdev_controller_get_drvdata(const struct serdev_controller *ctrl)
+{
+	return ctrl ? dev_get_drvdata(&ctrl->dev) : NULL;
+}
+
+static inline void serdev_controller_set_drvdata(struct serdev_controller *ctrl,
+					       void *data)
+{
+	dev_set_drvdata(&ctrl->dev, data);
+}
+
+/**
+ * serdev_controller_put() - decrement controller refcount
+ * @ctrl	serdev controller.
+ */
+static inline void serdev_controller_put(struct serdev_controller *ctrl)
+{
+	if (ctrl)
+		put_device(&ctrl->dev);
+}
+
+struct serdev_device *serdev_device_alloc(struct serdev_controller *);
+int serdev_device_add(struct serdev_device *);
+void serdev_device_remove(struct serdev_device *);
+
+struct serdev_controller *serdev_controller_alloc(struct device *, size_t);
+int serdev_controller_add(struct serdev_controller *);
+void serdev_controller_remove(struct serdev_controller *);
+
+static inline void serdev_controller_write_wakeup(struct serdev_controller *ctrl)
+{
+	struct serdev_device *serdev = ctrl->serdev;
+
+	if (!serdev || !serdev->ops->write_wakeup)
+		return;
+
+	serdev->ops->write_wakeup(ctrl->serdev);
+}
+
+static inline int serdev_controller_receive_buf(struct serdev_controller *ctrl,
+					      const unsigned char *data,
+					      size_t count)
+{
+	struct serdev_device *serdev = ctrl->serdev;
+
+	if (!serdev || !serdev->ops->receive_buf)
+		return -EINVAL;
+
+	return serdev->ops->receive_buf(ctrl->serdev, data, count);
+}
+
+#if IS_ENABLED(CONFIG_SERIAL_DEV_BUS)
+
+int serdev_device_open(struct serdev_device *);
+void serdev_device_close(struct serdev_device *);
+unsigned int serdev_device_set_baudrate(struct serdev_device *, unsigned int);
+void serdev_device_set_flow_control(struct serdev_device *, bool);
+int serdev_device_write_buf(struct serdev_device *, const unsigned char *, size_t);
+void serdev_device_write_flush(struct serdev_device *);
+int serdev_device_write_room(struct serdev_device *);
+
+/*
+ * serdev device driver functions
+ */
+int __serdev_device_driver_register(struct serdev_device_driver *, struct module *);
+#define serdev_device_driver_register(sdrv) \
+	__serdev_device_driver_register(sdrv, THIS_MODULE)
+
+/**
+ * serdev_device_driver_unregister() - unregister an serdev client driver
+ * @sdrv:	the driver to unregister
+ */
+static inline void serdev_device_driver_unregister(struct serdev_device_driver *sdrv)
+{
+	if (sdrv)
+		driver_unregister(&sdrv->driver);
+}
+
+#define module_serdev_device_driver(__serdev_device_driver) \
+	module_driver(__serdev_device_driver, serdev_device_driver_register, \
+			serdev_device_driver_unregister)
+
+#else
+
+static inline int serdev_device_open(struct serdev_device *sdev)
+{
+	return -ENODEV;
+}
+static inline void serdev_device_close(struct serdev_device *sdev) {}
+static inline unsigned int serdev_device_set_baudrate(struct serdev_device *sdev, unsigned int baudrate)
+{
+	return 0;
+}
+static inline void serdev_device_set_flow_control(struct serdev_device *sdev, bool enable) {}
+static inline int serdev_device_write_buf(struct serdev_device *sdev, const unsigned char *buf, size_t count)
+{
+	return -ENODEV;
+}
+static inline void serdev_device_write_flush(struct serdev_device *sdev) {}
+static inline int serdev_device_write_room(struct serdev_device *sdev)
+{
+	return 0;
+}
+
+#define serdev_device_driver_register(x)
+#define serdev_device_driver_unregister(x)
+
+#endif /* CONFIG_SERIAL_DEV_BUS */
+
+#endif /*_LINUX_SERDEV_H */