[RFC,1/3] uart bus: Introduce new bus for UART slave devices

diff --git a/drivers/Kconfig b/drivers/Kconfig
index e1e2066..9145494 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -202,4 +202,6 @@  source "drivers/hwtracing/intel_th/Kconfig"
 
 source "drivers/fpga/Kconfig"
 
+source "drivers/uart/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index 53abb4a..c915417 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -173,3 +173,4 @@  obj-$(CONFIG_STM)		+= hwtracing/stm/
 obj-$(CONFIG_ANDROID)		+= android/
 obj-$(CONFIG_NVMEM)		+= nvmem/
 obj-$(CONFIG_FPGA)		+= fpga/
+obj-$(CONFIG_UART_DEV)		+= uart/
diff --git a/drivers/uart/Kconfig b/drivers/uart/Kconfig
new file mode 100644
index 0000000..b232ce3
--- /dev/null
+++ b/drivers/uart/Kconfig
@@ -0,0 +1,17 @@ 
+#
+# UART slave driver configuration
+#
+menuconfig UART_DEV
+	tristate "UART device support"
+	help
+	  Support for devices connected via a UART
+
+if UART_DEV
+
+config UART_DEV_LOOPBACK
+	tristate "Loopback Test Driver"
+	help
+	  This option enables a loopback test driver. Anything received from
+	  the connected device will be echoed back.
+
+endif
diff --git a/drivers/uart/Makefile b/drivers/uart/Makefile
new file mode 100644
index 0000000..704eec0
--- /dev/null
+++ b/drivers/uart/Makefile
@@ -0,0 +1,3 @@ 
+obj-$(CONFIG_UART_DEV) := core.o
+
+obj-$(CONFIG_UART_DEV_LOOPBACK) += loopback.o
diff --git a/drivers/uart/core.c b/drivers/uart/core.c
new file mode 100644
index 0000000..5b5d0e1
--- /dev/null
+++ b/drivers/uart/core.c
@@ -0,0 +1,458 @@ 
+/*
+ * Copyright (C) 2016 Linaro Ltd.
+ * Author: Rob Herring <robh@kernel.org>
+ *
+ * Based on drivers/spmi/spmi.c:
+ * Copyright (c) 2012-2015, The Linux Foundation. All rights reserved.
+ *
+ * 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.
+ */
+#define DEBUG
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/idr.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/uart_device.h>
+#include <linux/pm_runtime.h>
+#include <linux/serial_core.h>
+
+static bool is_registered;
+static DEFINE_IDA(ctrl_ida);
+
+static void uart_dev_release(struct device *dev)
+{
+	struct uart_device *udev = to_uart_device(dev);
+	kfree(udev);
+}
+
+static const struct device_type uart_dev_type = {
+	.release	= uart_dev_release,
+};
+
+static void uart_ctrl_release(struct device *dev)
+{
+	struct uart_controller *ctrl = to_uart_controller(dev);
+	ida_simple_remove(&ctrl_ida, ctrl->nr);
+	kfree(ctrl);
+}
+
+static const struct device_type uart_ctrl_type = {
+	.release	= uart_ctrl_release,
+};
+
+static int uart_device_match(struct device *dev, struct device_driver *drv)
+{
+	if (of_driver_match_device(dev, drv))
+		return 1;
+
+	if (drv->name)
+		return strncmp(dev_name(dev), drv->name,
+			       SPMI_NAME_SIZE) == 0;
+
+	return 0;
+}
+
+/**
+ * uart_device_add() - add a device previously constructed via uart_device_alloc()
+ * @udev:	uart_device to be added
+ */
+int uart_device_add(struct uart_device *udev)
+{
+	struct uart_controller *ctrl = udev->ctrl;
+	int err;
+
+	dev_set_name(&udev->dev, "uartdev-%d", ctrl->nr);
+
+	err = device_add(&udev->dev);
+	if (err < 0) {
+		dev_err(&udev->dev, "Can't add %s, status %d\n",
+			dev_name(&udev->dev), err);
+		goto err_device_add;
+	}
+
+	dev_dbg(&udev->dev, "device %s registered\n", dev_name(&udev->dev));
+
+err_device_add:
+	return err;
+}
+EXPORT_SYMBOL_GPL(uart_device_add);
+
+/**
+ * uart_device_remove(): remove an SPMI device
+ * @udev:	uart_device to be removed
+ */
+void uart_device_remove(struct uart_device *udev)
+{
+	device_unregister(&udev->dev);
+}
+EXPORT_SYMBOL_GPL(uart_device_remove);
+
+int uart_dev_config(struct uart_device *udev, int baud, int parity, int bits, int flow)
+{
+	return uart_set_options(udev->ctrl->port, NULL, baud, parity, bits, flow);
+}
+
+int uart_dev_connect(struct uart_device *udev)
+{
+	unsigned long page;
+	struct uart_port *port = udev->ctrl->port;
+	struct uart_state *state = port->state;
+
+	WARN_ON(!state);
+
+	if (!state->xmit.buf) {
+		/* This is protected by the per port mutex */
+		page = get_zeroed_page(GFP_KERNEL);
+		if (!page)
+			return -ENOMEM;
+
+		state->xmit.buf = (unsigned char *) page;
+		uart_circ_clear(&state->xmit);
+	}
+
+	if (!udev->ctrl->recv.buf) {
+		/* This is protected by the per port mutex */
+		page = get_zeroed_page(GFP_KERNEL);
+		if (!page)
+			return -ENOMEM;
+
+		udev->ctrl->recv.buf = (unsigned char *) page;
+		uart_circ_clear(&udev->ctrl->recv);
+	}
+
+	if (port && port->ops->pm)
+		port->ops->pm(port, UART_PM_STATE_ON, state->pm_state);
+	state->pm_state = UART_PM_STATE_ON;
+
+	port->ops->set_mctrl(port, TIOCM_RTS | TIOCM_DTR);
+
+	return udev->ctrl->port->ops->startup(udev->ctrl->port);
+}
+
+int uart_dev_rx(struct uart_device *udev, u8 *buf, size_t count)
+{
+	struct uart_port *port = udev->ctrl->port;
+	struct uart_state *state = port->state;
+	struct circ_buf *circ = &udev->ctrl->recv;
+	int c, ret = 0;
+
+	if (!circ->buf)
+		return 0;
+
+	while (1) {
+		c = CIRC_CNT_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
+		if (count < c)
+			c = count;
+		if (c <= 0)
+			break;
+		memcpy(buf, circ->buf + circ->tail, c);
+		circ->tail = (circ->tail + c) & (PAGE_SIZE - 1);
+
+		buf += c;
+		count -= c;
+		ret += c;
+	}
+
+	return ret;
+}
+
+int uart_dev_tx(struct uart_device *udev, u8 *buf, size_t count)
+{
+	struct uart_port *port = udev->ctrl->port;
+	struct uart_state *state = port->state;
+	struct circ_buf *circ = &state->xmit;
+	unsigned long flags;
+	int c, ret = 0;
+
+	if (!circ->buf)
+		return 0;
+
+//	port = uart_port_lock(state, flags);
+	while (1) {
+		c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
+		if (count < c)
+			c = count;
+		if (c <= 0)
+			break;
+		memcpy(circ->buf + circ->head, buf, c);
+		circ->head = (circ->head + c) & (UART_XMIT_SIZE - 1);
+		buf += c;
+		count -= c;
+		ret += c;
+	}
+	port->ops->start_tx(port);
+
+//	uart_port_unlock(port, flags);
+
+	return ret;
+}
+
+
+static int uart_drv_probe(struct device *dev)
+{
+	const struct uart_dev_driver *sdrv = to_uart_dev_driver(dev->driver);
+	struct uart_device *udev = to_uart_device(dev);
+	int err;
+
+	pm_runtime_get_noresume(dev);
+	pm_runtime_set_active(dev);
+	pm_runtime_enable(dev);
+
+	err = sdrv->probe(udev);
+	if (err)
+		goto fail_probe;
+
+	return 0;
+
+fail_probe:
+	pm_runtime_disable(dev);
+	pm_runtime_set_suspended(dev);
+	pm_runtime_put_noidle(dev);
+	return err;
+}
+
+static int uart_drv_remove(struct device *dev)
+{
+	const struct uart_dev_driver *sdrv = to_uart_dev_driver(dev->driver);
+
+	pm_runtime_get_sync(dev);
+	sdrv->remove(to_uart_device(dev));
+	pm_runtime_put_noidle(dev);
+
+	pm_runtime_disable(dev);
+	pm_runtime_set_suspended(dev);
+	pm_runtime_put_noidle(dev);
+	return 0;
+}
+
+static struct bus_type uart_bus_type = {
+	.name		= "uart",
+	.match		= uart_device_match,
+	.probe		= uart_drv_probe,
+	.remove		= uart_drv_remove,
+};
+
+/**
+ * uart_controller_alloc() - Allocate a new SPMI device
+ * @ctrl:	associated controller
+ *
+ * Caller is responsible for either calling uart_device_add() to add the
+ * newly allocated controller, or calling uart_device_put() to discard it.
+ */
+struct uart_device *uart_device_alloc(struct uart_controller *ctrl)
+{
+	struct uart_device *udev;
+
+	udev = kzalloc(sizeof(*udev), GFP_KERNEL);
+	if (!udev)
+		return NULL;
+
+	udev->ctrl = ctrl;
+	device_initialize(&udev->dev);
+	udev->dev.parent = &ctrl->dev;
+	udev->dev.bus = &uart_bus_type;
+	udev->dev.type = &uart_dev_type;
+	return udev;
+}
+EXPORT_SYMBOL_GPL(uart_device_alloc);
+
+/**
+ * uart_controller_alloc() - Allocate a new SPMI controller
+ * @parent:	parent device
+ * @size:	size of private data
+ *
+ * Caller is responsible for either calling uart_controller_add() to add the
+ * newly allocated controller, or calling uart_controller_put() to discard it.
+ * The allocated private data region may be accessed via
+ * uart_controller_get_drvdata()
+ */
+struct uart_controller *uart_controller_alloc(struct device *parent,
+					      size_t size)
+{
+	struct uart_controller *ctrl;
+	int id;
+
+	if (WARN_ON(!parent))
+		return NULL;
+
+	ctrl = kzalloc(sizeof(*ctrl) + size, GFP_KERNEL);
+	if (!ctrl)
+		return NULL;
+
+	device_initialize(&ctrl->dev);
+	ctrl->dev.type = &uart_ctrl_type;
+	ctrl->dev.bus = &uart_bus_type;
+	ctrl->dev.parent = parent;
+	ctrl->dev.of_node = parent->of_node;
+	uart_controller_set_drvdata(ctrl, &ctrl[1]);
+
+	id = ida_simple_get(&ctrl_ida, 0, 0, GFP_KERNEL);
+	if (id < 0) {
+		dev_err(parent,
+			"unable to allocate SPMI controller identifier.\n");
+		uart_controller_put(ctrl);
+		return NULL;
+	}
+
+	ctrl->nr = id;
+	dev_set_name(&ctrl->dev, "uart-%d", id);
+
+	dev_dbg(&ctrl->dev, "allocated controller 0x%p id %d\n", ctrl, id);
+	return ctrl;
+}
+EXPORT_SYMBOL_GPL(uart_controller_alloc);
+
+static void of_uart_register_devices(struct uart_controller *ctrl)
+{
+	struct device_node *node;
+	int err;
+
+	if (!ctrl->dev.of_node)
+		return;
+
+	for_each_available_child_of_node(ctrl->dev.of_node, node) {
+		struct uart_device *udev;
+		u32 reg[2];
+
+		dev_dbg(&ctrl->dev, "adding child %s\n", node->full_name);
+
+		udev = uart_device_alloc(ctrl);
+		if (!udev)
+			continue;
+
+		udev->dev.of_node = node;
+
+		err = uart_device_add(udev);
+		if (err) {
+			dev_err(&udev->dev,
+				"failure adding device. status %d\n", err);
+			uart_device_put(udev);
+		}
+	}
+}
+
+/**
+ * uart_controller_add() - Add an SPMI controller
+ * @ctrl:	controller to be registered.
+ *
+ * Register a controller previously allocated via uart_controller_alloc() with
+ * the SPMI core.
+ */
+int uart_controller_add(struct uart_controller *ctrl)
+{
+	int ret;
+
+	/* Can't register until after driver model init */
+	if (WARN_ON(!is_registered))
+		return -EAGAIN;
+
+	ret = device_add(&ctrl->dev);
+	if (ret)
+		return ret;
+
+	if (IS_ENABLED(CONFIG_OF))
+		of_uart_register_devices(ctrl);
+
+	dev_dbg(&ctrl->dev, "uart-%d registered: dev:%p\n",
+		ctrl->nr, &ctrl->dev);
+
+	return 0;
+};
+EXPORT_SYMBOL_GPL(uart_controller_add);
+
+int uart_controller_rx(struct uart_controller *ctrl, unsigned int ch)
+{
+	struct circ_buf *circ = &ctrl->recv;
+	unsigned long flags;
+	int c, ret = 0;
+
+	if (!circ->buf)
+		return -ENODEV;
+
+	c = CIRC_SPACE_TO_END(circ->head, circ->tail, PAGE_SIZE);
+	if (c <= 0)
+		return 0;
+
+	circ->buf[circ->head] = ch;
+	circ->head = (circ->head + 1) & (PAGE_SIZE - 1);
+
+	return 1;
+}
+
+/* Remove a device associated with a controller */
+static int uart_ctrl_remove_device(struct device *dev, void *data)
+{
+	struct uart_device *spmidev = to_uart_device(dev);
+	if (dev->type == &uart_dev_type)
+		uart_device_remove(spmidev);
+	return 0;
+}
+
+/**
+ * uart_controller_remove(): remove an SPMI controller
+ * @ctrl:	controller to remove
+ *
+ * Remove a SPMI controller.  Caller is responsible for calling
+ * uart_controller_put() to discard the allocated controller.
+ */
+void uart_controller_remove(struct uart_controller *ctrl)
+{
+	int dummy;
+
+	if (!ctrl)
+		return;
+
+	dummy = device_for_each_child(&ctrl->dev, NULL,
+				      uart_ctrl_remove_device);
+	device_del(&ctrl->dev);
+}
+EXPORT_SYMBOL_GPL(uart_controller_remove);
+
+/**
+ * uart_driver_register() - Register client driver with SPMI core
+ * @sdrv:	client driver to be associated with client-device.
+ *
+ * This API will register the client driver with the SPMI framework.
+ * It is typically called from the driver's module-init function.
+ */
+int __uart_dev_driver_register(struct uart_dev_driver *sdrv, struct module *owner)
+{
+	sdrv->driver.bus = &uart_bus_type;
+	sdrv->driver.owner = owner;
+	return driver_register(&sdrv->driver);
+}
+EXPORT_SYMBOL_GPL(__uart_driver_register);
+
+static void __exit uart_exit(void)
+{
+	bus_unregister(&uart_bus_type);
+}
+module_exit(uart_exit);
+
+static int __init uart_init(void)
+{
+	int ret;
+
+	ret = bus_register(&uart_bus_type);
+	if (ret)
+		return ret;
+
+	is_registered = true;
+	return 0;
+}
+postcore_initcall(uart_init);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("UART module");
+//MODULE_ALIAS("platform:spmi");
diff --git a/drivers/uart/loopback.c b/drivers/uart/loopback.c
new file mode 100644
index 0000000..80b7769
--- /dev/null
+++ b/drivers/uart/loopback.c
@@ -0,0 +1,72 @@ 
+/*
+ * Copyright (C) 2016 Linaro Ltd.
+ * Author: 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.
+ */
+
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/uart_device.h>
+#include <linux/workqueue.h>
+
+struct loopback_data {
+	struct uart_device *udev;
+	struct delayed_work work;
+};
+
+static void loopback_work(struct work_struct *work)
+{
+	struct loopback_data *data = container_of((struct delayed_work *)work, struct loopback_data, work);
+	struct uart_device *udev = data->udev;
+	int cnt;
+	char buf[64];
+
+	cnt = uart_dev_rx(udev, buf, sizeof(buf));
+	uart_dev_tx(udev, buf, cnt);
+
+	schedule_delayed_work(&data->work, 5);
+}
+
+static int loopback_probe(struct uart_device *udev)
+{
+	struct loopback_data *data;
+
+	data = devm_kzalloc(&udev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	data->udev = udev;
+
+	dev_info(&udev->dev, "loopback probe!!!\n");
+
+	uart_dev_connect(udev);
+	uart_dev_config(udev, 115200, 'n', 8, 0);
+
+
+	INIT_DELAYED_WORK(&data->work, loopback_work);
+	schedule_delayed_work(&data->work, 100);
+
+	return 0;
+}
+
+static const struct of_device_id loopback_of_match[] = {
+	{ .compatible = "loopback-uart", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, loopback_of_match);
+
+static struct uart_dev_driver loopback_driver = {
+	.probe = loopback_probe,
+	.driver	= {
+		.name	= "loopback-uart",
+		.of_match_table = of_match_ptr(loopback_of_match),
+	},
+};
+module_uart_dev_driver(loopback_driver);
diff --git a/include/linux/uart_device.h b/include/linux/uart_device.h
new file mode 100644
index 0000000..a91d778
--- /dev/null
+++ b/include/linux/uart_device.h
@@ -0,0 +1,163 @@ 
+/*
+ * Copyright (C) 2016 Linaro Ltd.
+ * Author: Rob Herring <robh@kernel.org>
+ *
+ * Based on include/linux/spmi.h:
+ * Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
+ *
+ * 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_UART_DEVICE_H
+#define _LINUX_UART_DEVICE_H
+
+#include <linux/types.h>
+#include <linux/device.h>
+#include <linux/circ_buf.h>
+#include <linux/mod_devicetable.h>
+
+/**
+ * struct uart_device - Basic representation of an SPMI device
+ * @dev:	Driver model representation of the device.
+ * @ctrl:	SPMI controller managing the bus hosting this device.
+ * @usid:	This devices' Unique Slave IDentifier.
+ */
+struct uart_device {
+	struct device		dev;
+	struct uart_controller	*ctrl;
+};
+
+static inline struct uart_device *to_uart_device(struct device *d)
+{
+	return container_of(d, struct uart_device, dev);
+}
+
+static inline void *uart_device_get_drvdata(const struct uart_device *sdev)
+{
+	return dev_get_drvdata(&sdev->dev);
+}
+
+static inline void uart_device_set_drvdata(struct uart_device *sdev, void *data)
+{
+	dev_set_drvdata(&sdev->dev, data);
+}
+
+struct uart_device *uart_device_alloc(struct uart_controller *ctrl);
+
+static inline void uart_device_put(struct uart_device *sdev)
+{
+	if (sdev)
+		put_device(&sdev->dev);
+}
+
+int uart_device_add(struct uart_device *sdev);
+
+void uart_device_remove(struct uart_device *sdev);
+
+struct uart_port;
+
+/**
+ * struct uart_controller - interface to the SPMI master controller
+ * @dev:	Driver model representation of the device.
+ * @nr:		board-specific number identifier for this controller/bus
+ * @cmd:	sends a non-data command sequence on the SPMI bus.
+ * @read_cmd:	sends a register read command sequence on the SPMI bus.
+ * @write_cmd:	sends a register write command sequence on the SPMI bus.
+ */
+struct uart_controller {
+	struct device		dev;
+	struct uart_port	*port;
+	unsigned int		nr;
+	struct circ_buf		recv;
+};
+
+static inline struct uart_controller *to_uart_controller(struct device *d)
+{
+	return container_of(d, struct uart_controller, dev);
+}
+
+static inline
+void *uart_controller_get_drvdata(const struct uart_controller *ctrl)
+{
+	return dev_get_drvdata(&ctrl->dev);
+}
+
+static inline void uart_controller_set_drvdata(struct uart_controller *ctrl,
+					       void *data)
+{
+	dev_set_drvdata(&ctrl->dev, data);
+}
+
+struct uart_controller *uart_controller_alloc(struct device *parent,
+					      size_t size);
+
+/**
+ * uart_controller_put() - decrement controller refcount
+ * @ctrl	SPMI controller.
+ */
+static inline void uart_controller_put(struct uart_controller *ctrl)
+{
+	if (ctrl)
+		put_device(&ctrl->dev);
+}
+
+int uart_controller_add(struct uart_controller *ctrl);
+void uart_controller_remove(struct uart_controller *ctrl);
+
+int uart_controller_rx(struct uart_controller *ctrl, unsigned int ch);
+
+/**
+ * struct spmi_driver - SPMI slave device driver
+ * @driver:	SPMI device drivers should initialize name and owner field of
+ *		this structure.
+ * @probe:	binds this driver to a SPMI device.
+ * @remove:	unbinds this driver from the SPMI device.
+ *
+ * If PM runtime support is desired for a slave, a device driver can call
+ * pm_runtime_put() from their probe() routine (and a balancing
+ * pm_runtime_get() in remove()).  PM runtime support for a slave is
+ * implemented by issuing a SLEEP command to the slave on runtime_suspend(),
+ * transitioning the slave into the SLEEP state.  On runtime_resume(), a WAKEUP
+ * command is sent to the slave to bring it back to ACTIVE.
+ */
+struct uart_dev_driver {
+	struct device_driver driver;
+	int	(*probe)(struct uart_device *sdev);
+	void	(*remove)(struct uart_device *sdev);
+};
+
+static inline struct uart_dev_driver *to_uart_dev_driver(struct device_driver *d)
+{
+	return container_of(d, struct uart_dev_driver, driver);
+}
+
+#define uart_dev_driver_register(sdrv) \
+	__uart_dev_driver_register(sdrv, THIS_MODULE)
+int __uart_dev_driver_register(struct uart_dev_driver *sdrv, struct module *owner);
+
+/**
+ * spmi_driver_unregister() - unregister an SPMI client driver
+ * @sdrv:	the driver to unregister
+ */
+static inline void uart_dev_driver_unregister(struct uart_dev_driver *sdrv)
+{
+	if (sdrv)
+		driver_unregister(&sdrv->driver);
+}
+
+#define module_uart_dev_driver(__uart_dev_driver) \
+	module_driver(__uart_dev_driver, uart_dev_driver_register, \
+			uart_dev_driver_unregister)
+
+int uart_dev_config(struct uart_device *udev, int baud, int parity, int bits, int flow);
+int uart_dev_connect(struct uart_device *udev);
+int uart_dev_tx(struct uart_device *udev, u8 *buf, size_t count);
+int uart_dev_rx(struct uart_device *udev, u8 *buf, size_t count);
+
+#endif