Re: [PATCH 2/2] tty: add rpmsg driver

[xiang xiao]

On Thu, Mar 21, 2019 at 11:48 PM Fabien Dessenne <fabien.dessenne@xxxxxx> wrote:
>
> 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.
>

How to support multi-instances from the same remoteproc instance? I
saw that the channel name is fixed to "rpmsg-tty-channel" which mean
only one channel can be created for each remote side.

> 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);
> +

We need the flow control(or handshake) here, otherwise it's very easy
to lose the data if kernel keep send the data as fast as possible.

> +       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
>