Date:   Wed, 1 Apr 2020 12:06:18 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@...com>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, Suman Anna <s-anna@...com>,
        Fabien DESSENNE <fabien.dessenne@...com>,
        linux-stm32@...md-mailman.stormreply.com,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        xiang xiao <xiaoxiang781216@...il.com>
Subject: Re: [PATCH v7 2/2] tty: add rpmsg driver

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@...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@...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?  

> +		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.

> +			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?

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@...com>");
> +MODULE_DESCRIPTION("remote processor messaging tty driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.17.1
> 

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