On Thu 30 Sep 09:05 PDT 2021, Arnaud Pouliquen wrote:
> 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.
>
I think this looks pretty good, but it's a while since we discussed
this, reading your patches again makes me wonder:
1) With all the efforts related to virtualization and adding things such
as I2C support there, what are the merits of putting a tty driver ontop
of rpmsg in comparison with directly on virtio - which would be used for
virtualization as well.
2) What prevents you from pointing your userspace tool at an rpmsg_char
endpoint?
Thanks,
Bjorn
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxx>");
> +MODULE_DESCRIPTION("remote processor messaging tty driver");
> +MODULE_LICENSE("GPL v2");
> --
> 2.17.1
>
