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    SubjectRe: [PATCH v9 2/2] tty: add rpmsg driver
    On Fri, Oct 08, 2021 at 05:34:46PM +0200, 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@foss.st.com>
    >
    > ---
    > Update from V8
    > => Update based on Greg Greg Kroah-Hartman comments:
    > - add module name in kconfig
    > - remove the tty_rpmsg.rst documentation file and add description in
    > rpmsg_tty.c.
    > - rpmsg_tty.c remove of useless check and logs.
    > - print err log instead of debug log on truncated RX buffer.
    > ---
    > drivers/tty/Kconfig | 12 ++
    > drivers/tty/Makefile | 1 +
    > drivers/tty/rpmsg_tty.c | 275 ++++++++++++++++++++++++++++++++++++++++
    > 3 files changed, 288 insertions(+)
    > create mode 100644 drivers/tty/rpmsg_tty.c
    >
    > diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
    > index 23cc988c68a4..cc30ff93e2e4 100644
    > --- a/drivers/tty/Kconfig
    > +++ b/drivers/tty/Kconfig
    > @@ -368,6 +368,18 @@ 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.
    > +
    > + To compile this driver as a module, choose M here: the module will be
    > + called rpmsg_tty.
    > +
    > 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..226a13f6ef94
    > --- /dev/null
    > +++ b/drivers/tty/rpmsg_tty.c
    > @@ -0,0 +1,275 @@
    > +// SPDX-License-Identifier: GPL-2.0
    > +/*
    > + * Copyright (C) 2021 STMicroelectronics - All Rights Reserved
    > + *
    > + * 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 yet.
    > + */
    > +
    > +#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_err(&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);
    > +
    > + 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;
    > +
    > + 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);

    I'm with Greg on this one. Event if it's a dev_dbg() something like this could
    quickly fill the logs. Customers should learn to use ftrace. At the very least
    please use the ratelimited() version. Same comment applies to rpmsg_tty_cb().

    Otherwise:

    Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

    > + 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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