Re: [PATCH 1/1] tty: i3c: add tty over i3c master support

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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@xxxxxxx>
---

Notes:
     This patch depend on
     https://lore.kernel.org/imx/20231018205929.3435110-1-Frank.Li@xxxxxxx/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@xxxxxxx>
+ */
+
+#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!

+}
+
+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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