[PATCH 2/2] tty: add rpmsg driver

[Fabien Dessenne]

This driver exposes a standard tty interface on top of the rpmsg
framework through the "rpmsg-tty-channel" rpmsg service.

This driver supports multi-instances, offering a /dev/ttyRPMSGx entry
per rpmsg endpoint.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>
Signed-off-by: Fabien Dessenne <fabien.dessenne@xxxxxx>
---
 drivers/tty/Kconfig     |   9 ++
 drivers/tty/Makefile    |   1 +
 drivers/tty/rpmsg_tty.c | 309 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 319 insertions(+)
 create mode 100644 drivers/tty/rpmsg_tty.c

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 0840d27..42696e6 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -441,4 +441,13 @@ config VCC
 	depends on SUN_LDOMS
 	help
 	  Support for Sun logical domain consoles.
+
+config RPMSG_TTY
+	tristate "RPMSG tty driver"
+	depends on RPMSG
+	help
+	  Say y here to export rpmsg endpoints as tty devices, usually found
+	  in /dev/ttyRPMSGx.
+	  This makes it possible for user-space programs to send and receive
+	  rpmsg messages as a standard tty protocol.
 endif # TTY
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index c72cafd..90a98a2 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -33,5 +33,6 @@ obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o
 obj-$(CONFIG_GOLDFISH_TTY)	+= goldfish.o
 obj-$(CONFIG_MIPS_EJTAG_FDC_TTY) += mips_ejtag_fdc.o
 obj-$(CONFIG_VCC)		+= vcc.o
+obj-$(CONFIG_RPMSG_TTY)		+= rpmsg_tty.o
 
 obj-y += ipwireless/
diff --git a/drivers/tty/rpmsg_tty.c b/drivers/tty/rpmsg_tty.c
new file mode 100644
index 0000000..9c2a629
--- /dev/null
+++ b/drivers/tty/rpmsg_tty.c
@@ -0,0 +1,309 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) STMicroelectronics 2019 - All Rights Reserved
+ * Authors: Arnaud Pouliquen <arnaud.pouliquen@xxxxxx> for STMicroelectronics.
+ *          Fabien Dessenne <fabien.dessenne@xxxxxx> for STMicroelectronics.
+ * Derived from the imx-rpmsg and omap-rpmsg implementations.
+ */
+
+#include <linux/module.h>
+#include <linux/rpmsg.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+
+#define MAX_TTY_RPMSG		32
+
+static DEFINE_IDR(tty_idr);		/* tty instance id */
+static DEFINE_MUTEX(idr_lock);		/* protects tty_idr */
+
+static struct tty_driver *rpmsg_tty_driver;
+
+struct rpmsg_tty_port {
+	struct tty_port		port;	/* TTY port data */
+	unsigned int		id;	/* TTY rpmsg index */
+	spinlock_t		rx_lock; /* message reception lock */
+	struct rpmsg_device	*rpdev;	/* rpmsg device */
+};
+
+static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len,
+			void *priv, u32 src)
+{
+	int space;
+	unsigned char *cbuf;
+	struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);
+
+	dev_dbg(&rpdev->dev, "msg(<- src 0x%x) len %d\n", src, len);
+
+	print_hex_dump_debug(__func__, DUMP_PREFIX_NONE, 16, 1, data, len,
+			     true);
+
+	/* Flush the recv-ed none-zero data to tty node */
+	if (!len)
+		return -EINVAL;
+
+	spin_lock(&cport->rx_lock);
+	space = tty_prepare_flip_string(&cport->port, &cbuf, len);
+	if (space <= 0) {
+		dev_err(&rpdev->dev, "No memory for tty_prepare_flip_string\n");
+		spin_unlock(&cport->rx_lock);
+		return -ENOMEM;
+	}
+
+	if (space != len)
+		dev_warn(&rpdev->dev, "Trunc buffer from %d to %d\n",
+			 len, space);
+
+	memcpy(cbuf, data, space);
+	tty_flip_buffer_push(&cport->port);
+	spin_unlock(&cport->rx_lock);
+
+	return 0;
+}
+
+static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
+
+	if (!cport) {
+		dev_err(tty->dev, "cannot get cport\n");
+		return -ENODEV;
+	}
+
+	return tty_port_install(&cport->port, driver, tty);
+}
+
+static int rpmsg_tty_open(struct tty_struct *tty, struct file *filp)
+{
+	return tty_port_open(tty->port, tty, filp);
+}
+
+static void rpmsg_tty_close(struct tty_struct *tty, struct file *filp)
+{
+	return tty_port_close(tty->port, tty, filp);
+}
+
+static int rpmsg_tty_write(struct tty_struct *tty, const unsigned char *buf,
+			   int total)
+{
+	int count, ret = 0;
+	const unsigned char *tbuf;
+	struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
+	struct rpmsg_device *rpdev;
+	int msg_size;
+
+	if (!cport) {
+		dev_err(tty->dev, "cannot get cport\n");
+		return -ENODEV;
+	}
+
+	rpdev = cport->rpdev;
+
+	dev_dbg(&rpdev->dev, "%s: send message from tty->index = %d\n",
+		__func__, tty->index);
+
+	if (!buf) {
+		dev_err(&rpdev->dev, "buf shouldn't be null.\n");
+		return -ENOMEM;
+	}
+
+	msg_size = rpmsg_get_buf_payload_size(rpdev->ept);
+	if (msg_size < 0)
+		return msg_size;
+
+	count = total;
+	tbuf = buf;
+	do {
+		/* send a message to our remote processor */
+		ret = rpmsg_send(rpdev->ept, (void *)tbuf,
+				 min(count, msg_size));
+		if (ret) {
+			dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
+			return ret;
+		}
+
+		if (count > msg_size) {
+			count -= msg_size;
+			tbuf += msg_size;
+		} else {
+			count = 0;
+		}
+	} while (count > 0);
+
+	return total;
+}
+
+static int rpmsg_tty_write_room(struct tty_struct *tty)
+{
+	struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
+
+	if (!cport) {
+		dev_err(tty->dev, "cannot get cport\n");
+		return -ENODEV;
+	}
+
+	/* report the space in the rpmsg buffer */
+	return rpmsg_get_buf_payload_size(cport->rpdev->ept);
+}
+
+static const struct tty_operations rpmsg_tty_ops = {
+	.install	= rpmsg_tty_install,
+	.open		= rpmsg_tty_open,
+	.close		= rpmsg_tty_close,
+	.write		= rpmsg_tty_write,
+	.write_room	= rpmsg_tty_write_room,
+};
+
+struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void)
+{
+	struct rpmsg_tty_port *cport;
+
+	cport = kzalloc(sizeof(*cport), GFP_KERNEL);
+	if (!cport)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_lock(&idr_lock);
+	cport->id = idr_alloc(&tty_idr, cport, 0, MAX_TTY_RPMSG, GFP_KERNEL);
+	mutex_unlock(&idr_lock);
+
+	if (cport->id < 0) {
+		kfree(cport);
+		return ERR_PTR(-ENOSPC);
+	}
+
+	return cport;
+}
+
+static void rpmsg_tty_release_cport(struct rpmsg_tty_port *cport)
+{
+	mutex_lock(&idr_lock);
+	idr_remove(&tty_idr, cport->id);
+	mutex_unlock(&idr_lock);
+
+	kfree(cport);
+}
+
+static int rpmsg_tty_probe(struct rpmsg_device *rpdev)
+{
+	struct rpmsg_tty_port *cport;
+	struct device *tty_dev;
+	int ret;
+
+	cport = rpmsg_tty_alloc_cport();
+	if (IS_ERR(cport)) {
+		dev_err(&rpdev->dev, "failed to alloc tty port\n");
+		return PTR_ERR(cport);
+	}
+
+	tty_port_init(&cport->port);
+	cport->port.low_latency = cport->port.flags | ASYNC_LOW_LATENCY;
+
+	tty_dev = tty_port_register_device(&cport->port, rpmsg_tty_driver,
+					   cport->id, &rpdev->dev);
+	if (IS_ERR(tty_dev)) {
+		dev_err(&rpdev->dev, "failed to register tty port\n");
+		ret = PTR_ERR(tty_dev);
+		goto err_destroy;
+	}
+
+	spin_lock_init(&cport->rx_lock);
+	cport->rpdev = rpdev;
+
+	dev_set_drvdata(&rpdev->dev, cport);
+
+	dev_info(&rpdev->dev, "new channel: 0x%x -> 0x%x : ttyRPMSG%d\n",
+		 rpdev->src, rpdev->dst, cport->id);
+
+	return 0;
+
+err_destroy:
+	tty_port_destroy(&cport->port);
+	rpmsg_tty_release_cport(cport);
+	return ret;
+}
+
+static void rpmsg_tty_remove(struct rpmsg_device *rpdev)
+{
+	struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);
+
+	dev_info(&rpdev->dev, "removing rpmsg tty device %d\n", cport->id);
+
+	/* User hang up to release the tty */
+	if (tty_port_initialized(&cport->port))
+		tty_port_tty_hangup(&cport->port, false);
+
+	tty_unregister_device(rpmsg_tty_driver, cport->id);
+	tty_port_destroy(&cport->port);
+
+	rpmsg_tty_release_cport(cport);
+}
+
+static struct rpmsg_device_id rpmsg_driver_tty_id_table[] = {
+	{ .name	= "rpmsg-tty-channel" },
+	{ },
+};
+MODULE_DEVICE_TABLE(rpmsg, rpmsg_driver_tty_id_table);
+
+static struct rpmsg_driver rpmsg_tty_rpmsg_drv = {
+	.drv.name	= KBUILD_MODNAME,
+	.id_table	= rpmsg_driver_tty_id_table,
+	.probe		= rpmsg_tty_probe,
+	.callback	= rpmsg_tty_cb,
+	.remove		= rpmsg_tty_remove,
+};
+
+static int __init rpmsg_tty_init(void)
+{
+	int err;
+
+	rpmsg_tty_driver = tty_alloc_driver(MAX_TTY_RPMSG, TTY_DRIVER_REAL_RAW |
+					    TTY_DRIVER_DYNAMIC_DEV);
+	if (IS_ERR(rpmsg_tty_driver))
+		return PTR_ERR(rpmsg_tty_driver);
+
+	rpmsg_tty_driver->driver_name = "rpmsg_tty";
+	rpmsg_tty_driver->name = "ttyRPMSG";
+	rpmsg_tty_driver->major = 0;
+	rpmsg_tty_driver->type = TTY_DRIVER_TYPE_CONSOLE;
+	rpmsg_tty_driver->init_termios = tty_std_termios;
+
+	tty_set_operations(rpmsg_tty_driver, &rpmsg_tty_ops);
+
+	err = tty_register_driver(rpmsg_tty_driver);
+	if (err < 0) {
+		pr_err("Couldn't install rpmsg tty driver: err %d\n", err);
+		goto error_put;
+	}
+
+	err = register_rpmsg_driver(&rpmsg_tty_rpmsg_drv);
+	if (err < 0) {
+		pr_err("Couldn't register rpmsg tty driver: err %d\n", err);
+		goto error_unregister;
+	}
+
+	return 0;
+
+error_unregister:
+	tty_unregister_driver(rpmsg_tty_driver);
+
+error_put:
+	put_tty_driver(rpmsg_tty_driver);
+
+	return err;
+}
+
+static void __exit rpmsg_tty_exit(void)
+{
+	unregister_rpmsg_driver(&rpmsg_tty_rpmsg_drv);
+	tty_unregister_driver(rpmsg_tty_driver);
+	put_tty_driver(rpmsg_tty_driver);
+	idr_destroy(&tty_idr);
+}
+
+module_init(rpmsg_tty_init);
+module_exit(rpmsg_tty_exit);
+
+MODULE_AUTHOR("Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>");
+MODULE_AUTHOR("Fabien Dessenne <fabien.dessenne@xxxxxx>");
+MODULE_DESCRIPTION("virtio remote processor messaging tty driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4