Date:   Thu, 19 Oct 2023 16:21:34 -0400
From:   Frank Li <Frank.li@....com>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:TTY LAYER AND SERIAL DRIVERS" 
        <linux-serial@...r.kernel.org>, alexandre.belloni@...tlin.com,
        conor.culhane@...vaco.com, imx@...ts.linux.dev, joe@...ches.com,
        linux-i3c@...ts.infradead.org, miquel.raynal@...tlin.com
Subject: Re: [PATCH 1/1] tty: i3c: add tty over i3c master support

On Thu, Oct 19, 2023 at 09:12:58AM +0200, Jiri Slaby wrote:
> On 18. 10. 23, 23:11, Frank Li wrote:
> > Add new driver to allow tty over i3c master.
> 
> What is it good for? Why we should consider this for inclusion at all?
> 
> > Signed-off-by: Frank Li <Frank.Li@....com>
> > ---
> > 
> > Notes:
> >      This patch depend on
> >      https://lore.kernel.org/imx/20231018205929.3435110-1-Frank.Li@nxp.com/T/#t
> > 
> >   drivers/tty/Kconfig   |   8 +
> >   drivers/tty/Makefile  |   1 +
> >   drivers/tty/i3c_tty.c | 466 ++++++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 475 insertions(+)
> >   create mode 100644 drivers/tty/i3c_tty.c
> > 
> > diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> > index 5646dc6242cd9..6d91fe6a211a1 100644
> > --- a/drivers/tty/Kconfig
> > +++ b/drivers/tty/Kconfig
> > @@ -412,6 +412,14 @@ config RPMSG_TTY
> >   	  To compile this driver as a module, choose M here: the module will be
> >   	  called rpmsg_tty.
> > +config I3C_TTY
> > +	tristate "tty over i3c"
> 
> "TTY over I3C"
> 
> > +	depends on I3C
> > +	help
> > +	  Select this options if you'd like use tty over I3C master controller
> 
> TTY and add a period.
> 
> > --- /dev/null
> > +++ b/drivers/tty/i3c_tty.c
> > @@ -0,0 +1,466 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2023 NXP.
> > + *
> > + * Author: Frank Li <Frank.Li@....com>
> > + */
> > +
> > +#include <linux/delay.h>
> > +#include <linux/kernel.h>
> > +#include <linux/mod_devicetable.h>
> > +#include <linux/module.h>
> > +#include <linux/i3c/device.h>
> > +#include <linux/i3c/master.h>
> > +#include <linux/slab.h>
> > +#include <linux/console.h>
> > +#include <linux/serial_core.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/workqueue.h>
> > +#include <linux/tty_flip.h>
> > +
> > +static DEFINE_IDR(i3c_tty_minors);
> > +static DEFINE_MUTEX(i3c_tty_minors_lock);
> > +
> > +static struct tty_driver *i3c_tty_driver;
> > +
> > +#define I3C_TTY_MINORS		256
> > +#define I3C_TTY_TRANS_SIZE	16
> > +#define I3C_TTY_RX_STOP		BIT(0)
> > +#define I3C_TTY_RETRY		20
> > +#define I3C_TTY_YIELD_US	100
> > +
> > +struct ttyi3c_port {
> > +	struct tty_port port;
> > +	int minor;
> > +	unsigned int txfifo_size;
> > +	unsigned int rxfifo_size;
> > +	struct circ_buf xmit;
> 
> Why can't you use port.xmit_fifo?
> 
> > +	spinlock_t xlock; /* protect xmit */
> > +	void *buffer;
> > +	struct i3c_device *i3cdev;
> > +	struct work_struct txwork;
> > +	struct work_struct rxwork;
> > +	struct completion txcomplete;
> > +	struct workqueue_struct *workqueue;
> 
> Why do you need a special wq? And even, why per port?
> 
> > +	atomic_t status;
> > +};
> > +
> > +static const struct i3c_device_id i3c_ids[] = {
> > +	I3C_DEVICE(0x011B, 0x1000, NULL),
> > +	{ /* sentinel */ },
> > +};
> > +
> > +static int i3c_port_activate(struct tty_port *port, struct tty_struct *tty)
> > +{
> > +	struct ttyi3c_port *sport = container_of(port, struct ttyi3c_port, port);
> > +
> > +	atomic_set(&sport->status, 0);
> > +
> > +	return i3c_device_enable_ibi(sport->i3cdev);
> > +}
> > +
> > +static void i3c_port_shutdown(struct tty_port *port)
> > +{
> > +	struct ttyi3c_port *sport =
> > +		container_of(port, struct ttyi3c_port, port);
> > +
> > +	i3c_device_disable_ibi(sport->i3cdev);
> > +}
> > +
> > +static void i3c_port_destruct(struct tty_port *port)
> > +{
> > +	struct ttyi3c_port *sport =
> > +		container_of(port, struct ttyi3c_port, port);
> > +
> > +	mutex_lock(&i3c_tty_minors_lock);
> > +	idr_remove(&i3c_tty_minors, sport->minor);
> > +	mutex_unlock(&i3c_tty_minors_lock);
> > +}
> > +
> > +static const struct tty_port_operations i3c_port_ops = {
> > +	.shutdown = i3c_port_shutdown,
> > +	.activate = i3c_port_activate,
> > +	.destruct = i3c_port_destruct,
> > +};
> > +
> > +static struct ttyi3c_port *i3c_get_by_minor(unsigned int minor)
> > +{
> > +	struct ttyi3c_port *sport;
> > +
> > +	mutex_lock(&i3c_tty_minors_lock);
> > +	sport = idr_find(&i3c_tty_minors, minor);
> > +	mutex_unlock(&i3c_tty_minors_lock);
> > +
> > +	return sport;
> > +}
> > +
> > +static int i3c_install(struct tty_driver *driver, struct tty_struct *tty)
> > +{
> > +	struct ttyi3c_port *sport;
> > +	int ret;
> > +
> > +	sport = i3c_get_by_minor(tty->index);
> > +	if (!sport)
> > +		return -ENODEV;
> > +
> > +	ret = tty_standard_install(driver, tty);
> > +	if (ret)
> > +		return ret;
> > +
> > +	tty->driver_data = sport;
> > +
> > +	return 0;
> > +}
> 
> You don't need this at all. (Watch for XXX marks below.)
> 
> > +static ssize_t i3c_write(struct tty_struct *tty, const unsigned char *buf, size_t count)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +	struct circ_buf *circ = &sport->xmit;
> > +	unsigned long flags;
> > +	int c, ret = 0;
> > +
> > +	spin_lock_irqsave(&sport->xlock, flags);
> > +	while (1) {
> > +		c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
> > +		if (count < c)
> > +			c = count;
> > +		if (c <= 0)
> > +			break;
> > +
> > +		memcpy(circ->buf + circ->head, buf, c);
> > +		circ->head = (circ->head + c) & (UART_XMIT_SIZE - 1);
> > +		buf += c;
> > +		count -= c;
> > +		ret += c;
> > +	}
> > +	spin_unlock_irqrestore(&sport->xlock, flags);
> 
> With kfifo, all this would be one line, right?
> 
> > +
> > +	if (circ->head != circ->tail)
> > +		queue_work(sport->workqueue, &sport->txwork);
> > +
> > +	return ret;
> > +}
> > +
> > +static int i3c_put_char(struct tty_struct *tty, unsigned char ch)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +	struct circ_buf *circ = &sport->xmit;
> > +	unsigned long flags;
> > +	int ret = 0;
> > +
> > +	spin_lock_irqsave(&sport->xlock, flags);
> > +
> > +	if (sport && CIRC_SPACE(circ->head, circ->tail, UART_XMIT_SIZE) != 0) {
> > +		circ->buf[circ->head] = ch;
> > +		circ->head = (circ->head + 1) & (UART_XMIT_SIZE - 1);
> > +		ret = 1;
> > +	}
> > +
> > +	spin_unlock_irqrestore(&sport->xlock, flags);
> > +
> > +	return ret;
> > +}
> > +
> > +static void i3c_flush_chars(struct tty_struct *tty)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +
> > +	queue_work(sport->workqueue, &sport->txwork);
> > +}
> > +
> > +static unsigned int i3c_write_room(struct tty_struct *tty)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +	struct circ_buf *circ = &sport->xmit;
> > +	unsigned long flags;
> > +	int ret = 0;
> > +
> > +	spin_lock_irqsave(&sport->xlock, flags);
> > +	ret = CIRC_SPACE(circ->head, circ->tail, UART_XMIT_SIZE);
> > +	spin_unlock_irqrestore(&sport->xlock, flags);
> > +
> > +	return ret;
> > +}
> > +
> > +static void i3c_throttle(struct tty_struct *tty)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +
> > +	atomic_or(I3C_TTY_RX_STOP, &sport->status);
> > +}
> > +
> > +static void i3c_unthrottle(struct tty_struct *tty)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +
> > +	atomic_andnot(I3C_TTY_RX_STOP, &sport->status);
> > +
> > +	queue_work(sport->workqueue, &sport->rxwork);
> > +}
> > +
> > +static int i3c_open(struct tty_struct *tty, struct file *filp)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> 
> XXX Here, you can simply do:
> 
> struct ttyi3c_port *sport = container_of(tty->port, struct ttyi3c_port,
> port);
> 
> tty->driver_data = sport;
> 
> 
> > +	return tty_port_open(&sport->port, tty, filp);
> > +}
> > +
> > +static void i3c_close(struct tty_struct *tty, struct file *filp)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +
> > +	if (!sport)
> > +		return;
> 
> How can that happen?
> 
> > +	tty_port_close(tty->port, tty, filp);
> > +}
> > +
> > +static void i3c_wait_until_sent(struct tty_struct *tty, int timeout)
> > +{
> > +	struct ttyi3c_port *sport = tty->driver_data;
> > +
> > +	wait_for_completion_timeout(&sport->txcomplete, timeout);
> > +	reinit_completion(&sport->txcomplete);
> 
> Does this work in parallel?
> 
> > +}
> > +
> > +static const struct tty_operations i3c_tty_ops = {
> > +	.install = i3c_install,
> > +	.open = i3c_open,
> > +	.close = i3c_close,
> > +	.write = i3c_write,
> > +	.put_char = i3c_put_char,
> > +	.flush_chars = i3c_flush_chars,
> > +	.write_room = i3c_write_room,
> > +	.throttle = i3c_throttle,
> > +	.unthrottle = i3c_unthrottle,
> > +	.wait_until_sent = i3c_wait_until_sent,
> > +};
> > +
> > +static void i3c_controller_irq_handler(struct i3c_device *dev,
> > +				       const struct i3c_ibi_payload *payload)
> > +{
> > +	struct ttyi3c_port *sport = dev_get_drvdata(&dev->dev);
> > +
> > +	queue_work(sport->workqueue, &sport->rxwork);
> 
> Doesn't ibi provide threaded irqs? Oh, wait, i3c_master_handle_ibi() is
> already a work!

rxwork need be trigger by two sources: one from IBI irq, another is from
i3c_unthrottle(). 

If unthrottle just clear flags and IBI irq already missed, so rx will stop
work util new IBI coming.

I hope rxwork can continue to fetch left data. i3c_tty driver can't issue
a fake IBI here.

So using sperate rxwork. both IBI and unthrottle to trigger such work, make
rx can get all data from slave side.

Frank

> 
> > +}
> > +
> > +static void tty_i3c_rxwork(struct work_struct *work)
> > +{
> > +	struct ttyi3c_port *sport = container_of(work, struct ttyi3c_port, rxwork);
> > +	struct i3c_priv_xfer xfers;
> > +	int retry = I3C_TTY_RETRY;
> > +	u16 status = BIT(0);
> > +
> > +	do {
> > +		memset(&xfers, 0, sizeof(xfers));
> > +		xfers.data.in = sport->buffer;
> > +		xfers.len = I3C_TTY_TRANS_SIZE;
> > +		xfers.rnw = 1;
> > +
> > +		if (I3C_TTY_RX_STOP & atomic_read(&sport->status))
> 
> Hmm, why not much simpler (and yet atomic) {set,test,clear}_bit()?
> 
> > +			break;
> > +
> > +		i3c_device_do_priv_xfers(sport->i3cdev, &xfers, 1);
> > +
> > +		if (xfers.actual_len) {
> > +			tty_insert_flip_string(&sport->port, sport->buffer, xfers.actual_len);
> 
> This can fail.
> 
> > +			retry = 20;
> > +			continue;
> > +		} else {
> 
> "} else {" uneeded.
> 
> > +			status = BIT(0);
> > +			i3c_device_getstatus_format1(sport->i3cdev, &status);
> > +			/*
> > +			 * Target side need some time to fill data into fifo. Target side may not
> 
> "needs"
> 
> > +			 * have hardware update status in real time. Software update status always
> > +			 * need some delays.
> 
> "needs"
> 
> > +			 *
> > +			 * Generally, target side have cicular buffer in memory, it will be moved
> "circular" all around.
> 
> > +			 * into FIFO by CPU or DMA. 'status' just show if cicular buffer empty. But
> > +			 * there are gap, espcially CPU have not response irq to fill FIFO in time.
> 
> espcially
> 
> > +			 * So xfers.actual will be zero, wait for little time to avoid flood
> > +			 * transfer in i3c bus.
> > +			 */
> > +			usleep_range(I3C_TTY_YIELD_US, 10 * I3C_TTY_YIELD_US);
> > +			retry--;
> > +		}
> > +
> > +	} while (retry && (status & BIT(0)));
> > +
> > +	tty_flip_buffer_push(&sport->port);
> > +}
> > +
> > +static void tty_i3c_txwork(struct work_struct *work)
> > +{
> > +	struct ttyi3c_port *sport = container_of(work, struct ttyi3c_port, txwork);
> > +	struct circ_buf *circ = &sport->xmit;
> > +	int cnt = CIRC_CNT(circ->head, circ->tail, UART_XMIT_SIZE);
> > +	struct i3c_priv_xfer xfers;
> > +	int retry = I3C_TTY_RETRY;
> > +	unsigned long flags;
> > +	int actual;
> > +	int ret;
> > +
> > +	while (cnt > 0 && retry) {
> > +		xfers.rnw = 0;
> > +		xfers.len = CIRC_CNT_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
> > +		xfers.len = min_t(u16, 16, xfers.len);
> > +		xfers.data.out = circ->buf + circ->tail;
> > +
> > +		ret = i3c_device_do_priv_xfers(sport->i3cdev, &xfers, 1);
> > +		if (ret) {
> > +			/*
> > +			 * Target side may not move data out of FIFO. delay can't resolve problem,
> > +			 * just reduce some possiblity. Target can't end I3C SDR mode write
> > +			 * transfer, discard data is reasonable when FIFO overrun.
> > +			 */
> > +			usleep_range(I3C_TTY_YIELD_US, 10 * I3C_TTY_YIELD_US);
> > +			retry--;
> > +		} else {
> > +			retry = 0;
> > +		}
> > +
> > +		actual = xfers.len;
> > +
> > +		circ->tail = (circ->tail + actual) & (UART_XMIT_SIZE - 1);
> > +
> > +		if (CIRC_CNT(circ->head, circ->tail, UART_XMIT_SIZE) < WAKEUP_CHARS)
> > +			tty_port_tty_wakeup(&sport->port);
> > +
> > +		cnt = CIRC_CNT(circ->head, circ->tail, UART_XMIT_SIZE);
> > +	}
> > +
> > +	spin_lock_irqsave(&sport->xlock, flags);
> > +	if (circ->head == circ->tail)
> > +		complete(&sport->txcomplete);
> > +	spin_unlock_irqrestore(&sport->xlock, flags);
> > +}
> > +
> > +static int i3c_probe(struct i3c_device *i3cdev)
> > +{
> > +	struct ttyi3c_port *port;
> > +	struct device *tty_dev;
> > +	struct i3c_ibi_setup req;
> > +	int minor;
> > +	int ret;
> > +
> > +	port = devm_kzalloc(&i3cdev->dev, sizeof(*port), GFP_KERNEL);
> > +	if (!port)
> > +		return -ENOMEM;
> > +
> > +	port->i3cdev = i3cdev;
> > +	port->buffer = devm_kzalloc(&i3cdev->dev, UART_XMIT_SIZE, GFP_KERNEL);
> > +	if (!port->buffer)
> > +		return -ENOMEM;
> > +
> > +	port->xmit.buf = devm_kzalloc(&i3cdev->dev, UART_XMIT_SIZE, GFP_KERNEL);
> > +	if (!port->xmit.buf)
> > +		return -ENOMEM;
> 
> You allocate two pages even if you never use the device?
> 
> > +	dev_set_drvdata(&i3cdev->dev, port);
> > +
> > +	req.max_payload_len = 8;
> > +	req.num_slots = 4;
> > +	req.handler = &i3c_controller_irq_handler;
> > +
> > +	ret = i3c_device_request_ibi(i3cdev, &req);
> > +	if (ret)
> > +		return -EINVAL;
> > +
> > +	mutex_lock(&i3c_tty_minors_lock);
> > +	minor = idr_alloc(&i3c_tty_minors, port, 0, I3C_TTY_MINORS, GFP_KERNEL);
> > +	mutex_unlock(&i3c_tty_minors_lock);
> > +
> > +	if (minor < 0)
> > +		return -EINVAL;
> > +
> > +	spin_lock_init(&port->xlock);
> > +	INIT_WORK(&port->txwork, tty_i3c_txwork);
> > +	INIT_WORK(&port->rxwork, tty_i3c_rxwork);
> > +	init_completion(&port->txcomplete);
> > +
> > +	port->workqueue = alloc_workqueue("%s", 0, 0, dev_name(&i3cdev->dev));
> > +	if (!port->workqueue)
> > +		return -ENOMEM;
> > +
> > +	tty_port_init(&port->port);
> > +	port->port.ops = &i3c_port_ops;
> > +
> > +	tty_dev = tty_port_register_device(&port->port, i3c_tty_driver, minor,
> > +					   &i3cdev->dev);
> > +	if (IS_ERR(tty_dev)) {
> > +		destroy_workqueue(port->workqueue);
> 
> What about tty_port_put() (it drops the idr too)? And free ibi?
> 
> > +		return PTR_ERR(tty_dev);
> > +	}
> > +
> > +	port->minor = minor;
> > +
> > +	return 0;
> > +}
> > +
> > +void i3c_remove(struct i3c_device *dev)
> > +{
> > +	struct ttyi3c_port *sport = dev_get_drvdata(&dev->dev);
> > +
> > +	tty_port_unregister_device(&sport->port, i3c_tty_driver, sport->minor);
> > +	cancel_work_sync(&sport->txwork);
> > +	destroy_workqueue(sport->workqueue);
> 
> The same as above.
> 
> > +}
> > +
> > +static struct i3c_driver i3c_driver = {
> > +	.driver = {
> > +		.name = "ttyi3c",
> > +	},
> > +	.probe = i3c_probe,
> > +	.remove = i3c_remove,
> > +	.id_table = i3c_ids,
> > +};
> > +
> > +static int __init i3c_tty_init(void)
> > +{
> > +	int ret;
> > +
> > +	i3c_tty_driver = tty_alloc_driver(I3C_TTY_MINORS,
> > +					  TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV);
> > +
> > +	if (IS_ERR(i3c_tty_driver))
> > +		return PTR_ERR(i3c_tty_driver);
> > +
> > +	i3c_tty_driver->driver_name = "ttyI3C";
> > +	i3c_tty_driver->name = "ttyI3C";
> > +	i3c_tty_driver->minor_start = 0,
> > +	i3c_tty_driver->type = TTY_DRIVER_TYPE_SERIAL,
> > +	i3c_tty_driver->subtype = SERIAL_TYPE_NORMAL,
> > +	i3c_tty_driver->init_termios = tty_std_termios;
> > +	i3c_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL |
> > +					       CLOCAL;
> > +	i3c_tty_driver->init_termios.c_lflag = 0;
> > +
> > +	tty_set_operations(i3c_tty_driver, &i3c_tty_ops);
> > +
> > +	ret = tty_register_driver(i3c_tty_driver);
> > +	if (ret) {
> > +		tty_driver_kref_put(i3c_tty_driver);
> > +		return ret;
> > +	}
> > +
> > +	ret = i3c_driver_register(&i3c_driver);
> > +	if (ret) {
> > +		tty_unregister_driver(i3c_tty_driver);
> > +		tty_driver_kref_put(i3c_tty_driver);
> 
> Use goto + fail paths. And in i3c_probe() too.
> 
> > +	}
> > +
> > +	return ret;
> > +}
> 
> 
> regards,
> -- 
> js
> suse labs
> 

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