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SubjectRe: [PATCH v7 2/2] tty: add rpmsg driver
On Thu, 2 Apr 2020 at 09:25, Arnaud POULIQUEN <arnaud.pouliquen@st.com> wrote:
>
> Hi Mathieu,
>
> On 4/1/20 8:06 PM, Mathieu Poirier wrote:
> > On Tue, Mar 24, 2020 at 06:04:07PM +0100, 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.
> >>
> >> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
> >> ---
> >> Documentation/serial/tty_rpmsg.rst | 45 ++++
> >> drivers/tty/Kconfig | 9 +
> >> drivers/tty/Makefile | 1 +
> >> drivers/tty/rpmsg_tty.c | 417 +++++++++++++++++++++++++++++
> >> 4 files changed, 472 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..fc1d3fba73c5
> >> --- /dev/null
> >> +++ b/Documentation/serial/tty_rpmsg.rst
> >> @@ -0,0 +1,45 @@
> >> +.. SPDX-License-Identifier: GPL-2.0
> >> +
> >> +=============
> >> +The 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-raw" RPMsg service, for TTY raw data support without flow control
> >> +- a "rpmsg-tty-ctrl" RPMSg service, for TTY support with flow control.
> >> +
> >> +Information related to the RPMsg and associated tty device is available in
> >> +/sys/bus/rpmsg/devices/.
> >> +
> >> +RPMsg TTY without control
> >> +---------------------
> >> +
> >> +The default end point associated with the "rpmsg-tty-raw" service is directly
> >> +used for data exchange. No flow control is available.
> >> +
> >> +To be compliant with this driver, the remote firmware must create its data end point associated with the "rpmsg-tty-raw" service.
> >> +
> >> +RPMsg TTY with control
> >> +---------------------
> >> +
> >> +The default end point associated with the "rpmsg-tty-ctrl" service is reserved for
> >> +the control. A second endpoint must be created for data exchange.
> >> +
> >> +The control channel is used to transmit to the remote processor the CTS status,
> >> +as well as the end point address for data transfer.
> >> +
> >> +To be compatible with this driver, the remote firmware must create or use its end point associated with "rpmsg-tty-ctrl" service, plus a second endpoint for the data flow.
> >> +On Linux rpmsg_tty probes, the data endpoint address and the CTS (set to disable)
> >> +is sent to the remote processor.
> >> +The remote processor has to respect following rules:
> >> +- It only transmits data when Linux remote cts is enable, otherwise message
> >> + could be lost.
> >> +- It can pause/resume reception by sending a control message (rely on CTS state).
> >> +
> >> +Control message structure:
> >> +struct rpmsg_tty_ctrl {
> >> + u8 cts; /* remote reception status */
> >> + u16 d_ept_addr; /* data endpoint address */
> >> +};
> >> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> >> index a312cb33a99b..9d3ff6df9f25 100644
> >> --- a/drivers/tty/Kconfig
> >> +++ b/drivers/tty/Kconfig
> >> @@ -454,6 +454,15 @@ config VCC
> >> 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.
> >> +
> >> config LDISC_AUTOLOAD
> >> bool "Automatically load TTY Line Disciplines"
> >> default y
> >> diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
> >> index 020b1cd9294f..c2465e7ebc2a 100644
> >> --- a/drivers/tty/Makefile
> >> +++ b/drivers/tty/Makefile
> >> @@ -34,5 +34,6 @@ 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..49ce3b72781a
> >> --- /dev/null
> >> +++ b/drivers/tty/rpmsg_tty.c
> >> @@ -0,0 +1,417 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +/*
> >> + * Copyright (C) STMicroelectronics 2020 - All Rights Reserved
> >> + * Authors: Arnaud Pouliquen <arnaud.pouliquen@st.com> for STMicroelectronics.
> >> + */
> >> +
> >> +#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
> >> +
> >> +#define TTY_CH_NAME_RAW "rpmsg-tty-raw"
> >> +#define TTY_CH_NAME_WITH_CTS "rpmsg-tty-ctrl"
> >> +
> >> +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_ctrl {
> >> + u16 d_ept_addr; /* data endpoint address */
> >> + u8 cts; /* remote reception status */
> >> +} __packed;
> >> +
> >> +struct rpmsg_tty_port {
> >> + struct tty_port port; /* TTY port data */
> >> + int id; /* TTY rpmsg index */
> >> + bool cts; /* remote reception status */
> >> + struct rpmsg_device *rpdev; /* rpmsg device */
> >> + struct rpmsg_endpoint *cs_ept; /* channel control endpoint */
> >> + struct rpmsg_endpoint *d_ept; /* data endpoint */
> >> + u32 data_dst; /* data destination endpoint address */
> >> +};
> >> +
> >> +typedef void (*rpmsg_tty_rx_cb_t)(struct rpmsg_device *, void *, int, void *,
> >> + u32);
> >> +
> >> +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 (src == cport->data_dst) {
> >> + /* data message */
> >> + if (!len)
> >> + return -EINVAL;
> >> + copied = tty_insert_flip_string_fixed_flag(&cport->port, data,
> >> + TTY_NORMAL, len);
> >> + if (copied != len)
> >> + dev_dbg(&rpdev->dev, "trunc buffer: available space is %d\n",
> >> + copied);
> >> + tty_flip_buffer_push(&cport->port);
> >> + } else {
> >> + /* control message */
> >> + struct rpmsg_tty_ctrl *msg = data;
> >> +
> >> + if (len != sizeof(*msg))
> >> + return -EINVAL;
> >> +
> >> + cport->data_dst = msg->d_ept_addr;
> >> +
> >> + /* Update remote cts state */
> >> + cport->cts = msg->cts ? 1 : 0;
> >> +
> >> + if (cport->cts)
> >> + tty_port_tty_wakeup(&cport->port);
> >> + }
> >> +
> >> + return 0;
> >> +}
> >> +
> >> +static void rpmsg_tty_send_term_ready(struct tty_struct *tty, u8 state)
> >> +{
> >> + struct rpmsg_tty_port *cport = tty->driver_data;
> >> + struct rpmsg_tty_ctrl m_ctrl;
> >> + int ret;
> >> +
> >> + m_ctrl.cts = state;
> >> + m_ctrl.d_ept_addr = cport->d_ept->addr;
> >> +
> >> + ret = rpmsg_trysend(cport->cs_ept, &m_ctrl, sizeof(m_ctrl));
> >> + if (ret < 0)
> >> + dev_dbg(tty->dev, "cannot send control (%d)\n", ret);
> >> +};
> >> +
> >> +static void rpmsg_tty_throttle(struct tty_struct *tty)
> >> +{
> >> + struct rpmsg_tty_port *cport = tty->driver_data;
> >> +
> >> + /* Disable remote transmission */
> >> + if (cport->cs_ept)
> >> + rpmsg_tty_send_term_ready(tty, 0);
> >> +};
> >> +
> >> +static void rpmsg_tty_unthrottle(struct tty_struct *tty)
> >> +{
> >> + struct rpmsg_tty_port *cport = tty->driver_data;
> >> +
> >> + /* Enable remote transmission */
> >> + if (cport->cs_ept)
> >> + rpmsg_tty_send_term_ready(tty, 1);
> >> +};
> >> +
> >> +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;
> >> + u8 *tmpbuf;
> >> +
> >> + /* If cts not set, the message is not sent*/
> >> + if (!cport->cts)
> >> + return 0;
> >> +
> >> + rpdev = cport->rpdev;
> >> +
> >> + dev_dbg(&rpdev->dev, "%s: send msg from tty->index = %d, len = %d\n",
> >> + __func__, tty->index, len);
> >> +
> >> + msg_max_size = rpmsg_get_mtu(rpdev->ept);
> >> +
> >> + msg_size = min(len, msg_max_size);
> >> + tmpbuf = kzalloc(msg_size, GFP_KERNEL);
> >> + if (!tmpbuf)
> >> + return -ENOMEM;
> >> +
> >> + memcpy(tmpbuf, buf, msg_size);
> >> +
> >> + /*
> >> + * Try to send the message to remote processor, if failed return 0 as
> >> + * no data sent
> >> + */
> >> + ret = rpmsg_trysendto(cport->d_ept, tmpbuf, msg_size, cport->data_dst);
> >> + kfree(tmpbuf);
> >> + if (ret) {
> >> + dev_dbg(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
> >> + return 0;
> >> + }
> >> +
> >> + return msg_size;
> >> +}
> >> +
> >> +static int rpmsg_tty_write_room(struct tty_struct *tty)
> >> +{
> >> + struct rpmsg_tty_port *cport = tty->driver_data;
> >> +
> >> + return cport->cts ? rpmsg_get_mtu(cport->rpdev->ept) : 0;
> >> +}
> >> +
> >> +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,
> >> + .throttle = rpmsg_tty_throttle,
> >> + .unthrottle = rpmsg_tty_unthrottle,
> >> +};
> >> +
> >> +static 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_port_activate(struct tty_port *p, struct tty_struct *tty)
> >> +{
> >> + p->low_latency = (p->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
> >> +
> >> + /* Allocate the buffer we use for writing data */
> >> + return tty_port_alloc_xmit_buf(p);
> >> +}
> >> +
> >> +static void rpmsg_tty_port_shutdown(struct tty_port *p)
> >> +{
> >> + /* Free the write buffer */
> >> + tty_port_free_xmit_buf(p);
> >> +}
> >> +
> >> +static void rpmsg_tty_dtr_rts(struct tty_port *port, int raise)
> >> +{
> >> + dev_dbg(port->tty->dev, "%s: dtr_rts state %d\n", __func__, raise);
> >> +
> >> + if (raise)
> >> + rpmsg_tty_unthrottle(port->tty);
> >> + else
> >> + rpmsg_tty_throttle(port->tty);
> >> +}
> >> +
> >> +static const struct tty_port_operations rpmsg_tty_port_ops = {
> >> + .activate = rpmsg_tty_port_activate,
> >> + .shutdown = rpmsg_tty_port_shutdown,
> >> + .dtr_rts = rpmsg_tty_dtr_rts,
> >> +};
> >> +
> >> +static int rpmsg_tty_probe(struct rpmsg_device *rpdev)
> >> +{
> >> + struct rpmsg_tty_port *cport;
> >> + struct device *dev = &rpdev->dev;
> >> + struct rpmsg_channel_info chinfo;
> >> + 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);
> >> + }
> >> +
> >> + if (!strncmp(rpdev->id.name, TTY_CH_NAME_WITH_CTS,
> >> + sizeof(TTY_CH_NAME_WITH_CTS))) {
> >> + /*
> >> + * the default endpoint is used for control. Create a second
> >> + * endpoint for the data that would be exchanges trough control
> >> + * endpoint. address of the data endpoint will be provided with
> >> + * the cts state
> >> + */
> >> + cport->cs_ept = rpdev->ept;
> >> + cport->data_dst = RPMSG_ADDR_ANY;
> >> +
> >> + strscpy(chinfo.name, TTY_CH_NAME_WITH_CTS, sizeof(chinfo.name));
> >
> > Shouldn't this be TTY_CH_NAME_RAW instead of TTY_CH_NAME_WITH_CTS?
> The TTY_CH_NAME_WITH_CTS represent here the service "TTY support with flow control"
> the aim here is to define 2 endpoints on top of the service channel.
> the main is used for the CTS control but also to exchange the addresses of the
> second endpoint that is used for the data flow.

Right - the new endpoint, the one that is about to be created using
"chinfo.name" is a data endpoint, hence the confusion.

> here if you associate the 2nd endpoint to a différent service name, you have no
> correlation between the control ept and the data endpoint ( at least if you
> want to support multi instance)
>
> I can probaly implement it in a different way using your path [1]
> by creating a correlation between the control and the data, based
> on the naming.
> something like:
> - "tty-featureA" /* data stream associated to featureA"
> - "tty-featureB" /* data stream associated to featureB"
> - "tty-ctl-featureB" /* control associated to featureB"

I would do "tty-featureB-ctrl". That way "tty-featureB" and
"tty-featureB-ctrl" always appear one after the other when doing an
"ls" on the command line.

>
> That would be probably more straight forward for users...
>
> [1] https://lkml.org/lkml/2020/2/12/1083
> >
> >> + chinfo.src = RPMSG_ADDR_ANY;
> >> + chinfo.dst = RPMSG_ADDR_ANY;
> >> +
> >> + cport->d_ept = rpmsg_create_ept(rpdev, rpmsg_tty_cb, cport,
> >> + chinfo);
> >> + if (!cport->d_ept) {
> >> + dev_err(dev, "failed to create tty control channel\n");
> >
> > Here too I don't understand why we are talking about the control channel when
> > the data channel is created. Am I missing something?
> >
> > Also I suggest function rpmsg_tty_cp() to be split, one for control and one for
> > data. That will make it easier to follow who processes what.
>
> you mean rpmsg_tty_probe? yes i will.

Splitting rpmsg_tty_probe() would be good too, but I was referring to
rpmsg_tty_cb().

>
> >
> >> + ret = -ENOMEM;
> >> + goto err_r_cport;
> >> + }
> >> + dev_dbg(dev, "%s: creating data endpoint with address %#x\n",
> >> + __func__, cport->d_ept->addr);
> >> + } else {
> >> + /*
> >> + * TTY over rpmsg without CTS management the default endpoint
> >> + * is use for raw data transmission.
> >> + */
> >> + cport->cs_ept = NULL;
> >> + cport->cts = 1;
> >> + cport->d_ept = rpdev->ept;
> >> + cport->data_dst = rpdev->dst;
> >> + }
> >> +
> >> + 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);
> >> + if (cport->cs_ept)
> >> + rpmsg_destroy_ept(cport->d_ept);
> >> +err_r_cport:
> >> + 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);
> >> + if (cport->cs_ept)
> >> + rpmsg_destroy_ept(cport->d_ept);
> >> + rpmsg_tty_release_cport(cport);
> >> +}
> >> +
> >> +static struct rpmsg_device_id rpmsg_driver_tty_id_table[] = {
> >> + { .name = TTY_CH_NAME_RAW },
> >> + { .name = TTY_CH_NAME_WITH_CTS},
> >
> > If I'm not mistaken support for more than one tty
> > per remote proc can't happen because of rpmsg_find_device() in
> > rpmsg_create_channel() - is this correct?
>
> There is not bloker to instantiate the same service several times.

You are correct. I took another look at rpmsg_device_match() and the
second condition [2] allows for channels to have the same name for as
long as the destination address is different.

[2]. https://elixir.bootlin.com/linux/v5.6/source/drivers/rpmsg/rpmsg_core.c#L299

> On remote side it is enough to create 2 endpoints with the same service
> name and with the destination address set to RPMSG_ADDR_ANY. This will
> trig 2 rpmsg_ns_cb, that will probe 2 times the device.
>
> As example please have a look to the stm32MP1 sample here which creates
> 2 tty rpmsg channels:
> https://github.com/STMicroelectronics/STM32CubeMP1/tree/master/Projects/STM32MP157C-DK2/Applications/OpenAMP/OpenAMP_TTY_echo
>
> Thanks,
> Arnaud
>
> >
> > Thanks,
> > Mathieu
> >
> >> + { },
> >> +};
> >> +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:
> >> + 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@st.com>");
> >> +MODULE_DESCRIPTION("remote processor messaging tty driver");
> >> +MODULE_LICENSE("GPL v2");
> >> --
> >> 2.17.1
> >>

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