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    Subject[PATCH v8 2/2] tty: add rpmsg driver
    Date
    This driver exposes a standard TTY interface on top of the rpmsg
    framework through a rpmsg service.

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

    Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
    ---
    Documentation/serial/tty_rpmsg.rst | 15 ++
    drivers/tty/Kconfig | 9 +
    drivers/tty/Makefile | 1 +
    drivers/tty/rpmsg_tty.c | 275 +++++++++++++++++++++++++++++
    4 files changed, 300 insertions(+)
    create mode 100644 Documentation/serial/tty_rpmsg.rst
    create mode 100644 drivers/tty/rpmsg_tty.c

    diff --git a/Documentation/serial/tty_rpmsg.rst b/Documentation/serial/tty_rpmsg.rst
    new file mode 100644
    index 000000000000..b055107866c9
    --- /dev/null
    +++ b/Documentation/serial/tty_rpmsg.rst
    @@ -0,0 +1,15 @@
    +.. SPDX-License-Identifier: GPL-2.0
    +
    +=========
    +RPMsg TTY
    +=========
    +
    +The rpmsg tty driver implements serial communication on the RPMsg bus to makes possible for
    +user-space programs to send and receive rpmsg messages as a standard tty protocol.
    +
    +The remote processor can instantiate a new tty by requesting a "rpmsg-tty" RPMsg service.
    +
    +The "rpmsg-tty" service is directly used for data exchange. No flow control is implemented.
    +
    +Information related to the RPMsg and associated tty device is available in
    +/sys/bus/rpmsg/devices/.
    diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
    index 23cc988c68a4..5095513029d7 100644
    --- a/drivers/tty/Kconfig
    +++ b/drivers/tty/Kconfig
    @@ -368,6 +368,15 @@ config VCC

    source "drivers/tty/hvc/Kconfig"

    +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

    source "drivers/tty/serdev/Kconfig"
    diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
    index a2bd75fbaaa4..07aca5184a55 100644
    --- a/drivers/tty/Makefile
    +++ b/drivers/tty/Makefile
    @@ -26,5 +26,6 @@ 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 000000000000..0c99f54c2911
    --- /dev/null
    +++ b/drivers/tty/rpmsg_tty.c
    @@ -0,0 +1,275 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/*
    + * Copyright (C) STMicroelectronics 2021 - All Rights Reserved
    + */
    +
    +#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 */
    + int id; /* TTY rpmsg index */
    + struct rpmsg_device *rpdev; /* rpmsg device */
    +};
    +
    +static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src)
    +{
    + struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);
    + int copied;
    +
    + if (!len)
    + return -EINVAL;
    + copied = tty_insert_flip_string(&cport->port, data, len);
    + if (copied != len)
    + dev_dbg(&rpdev->dev, "Trunc buffer: available space is %d\n",
    + copied);
    + tty_flip_buffer_push(&cport->port);
    +
    + 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;
    + }
    +
    + tty->driver_data = cport;
    +
    + 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 u8 *buf, int len)
    +{
    + struct rpmsg_tty_port *cport = tty->driver_data;
    + struct rpmsg_device *rpdev;
    + int msg_max_size, msg_size;
    + int ret;
    +
    + rpdev = cport->rpdev;
    +
    + dev_dbg(&rpdev->dev, "Send msg from tty->index = %d, len = %d\n", tty->index, len);
    +
    + msg_max_size = rpmsg_get_mtu(rpdev->ept);
    + if (msg_max_size < 0)
    + return msg_max_size;
    +
    + msg_size = min(len, msg_max_size);
    +
    + /*
    + * Use rpmsg_trysend instead of rpmsg_send to send the message so the caller is not
    + * hung until a rpmsg buffer is available. In such case rpmsg_trysend returns -ENOMEM.
    + */
    + ret = rpmsg_trysend(rpdev->ept, (void *)buf, msg_size);
    + if (ret) {
    + dev_dbg(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
    + return ret;
    + }
    +
    + return msg_size;
    +}
    +
    +static unsigned int rpmsg_tty_write_room(struct tty_struct *tty)
    +{
    + struct rpmsg_tty_port *cport = tty->driver_data;
    + int size;
    +
    + size = rpmsg_get_mtu(cport->rpdev->ept);
    + if (size < 0)
    + return 0;
    +
    + return size;
    +}
    +
    +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,
    +};
    +
    +static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void)
    +{
    + struct rpmsg_tty_port *cport;
    + int err;
    +
    + 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) {
    + err = cport->id;
    + kfree(cport);
    + return ERR_PTR(err);
    + }
    +
    + 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 const struct tty_port_operations rpmsg_tty_port_ops = { };
    +
    +static int rpmsg_tty_probe(struct rpmsg_device *rpdev)
    +{
    + struct rpmsg_tty_port *cport;
    + struct device *dev = &rpdev->dev;
    + struct device *tty_dev;
    + int ret;
    +
    + cport = rpmsg_tty_alloc_cport();
    + if (IS_ERR(cport)) {
    + dev_err(dev, "Failed to alloc tty port\n");
    + return PTR_ERR(cport);
    + }
    +
    + tty_port_init(&cport->port);
    + cport->port.ops = &rpmsg_tty_port_ops;
    +
    + tty_dev = tty_port_register_device(&cport->port, rpmsg_tty_driver,
    + cport->id, dev);
    + if (IS_ERR(tty_dev)) {
    + dev_err(dev, "Failed to register tty port\n");
    + ret = PTR_ERR(tty_dev);
    + goto err_destroy;
    + }
    +
    + cport->rpdev = rpdev;
    +
    + dev_set_drvdata(dev, cport);
    +
    + dev_dbg(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_dbg(&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" },
    + { },
    +};
    +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;
    +
    + /* Disable unused mode by default */
    + rpmsg_tty_driver->init_termios = tty_std_termios;
    + rpmsg_tty_driver->init_termios.c_lflag &= ~(ECHO | ICANON);
    + rpmsg_tty_driver->init_termios.c_oflag &= ~(OPOST | ONLCR);
    +
    + 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:
    + tty_driver_kref_put(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);
    + tty_driver_kref_put(rpmsg_tty_driver);
    + idr_destroy(&tty_idr);
    +}
    +
    +module_init(rpmsg_tty_init);
    +module_exit(rpmsg_tty_exit);
    +
    +MODULE_AUTHOR("Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>");
    +MODULE_DESCRIPTION("remote processor messaging tty driver");
    +MODULE_LICENSE("GPL v2");
    --
    2.17.1
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      Last update: 2021-09-30 18:14    [W:2.412 / U:0.016 seconds]
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