Re: [PATCH v5 1/2] usb: serial: add support for CH348

[Johan Hovold]

On Fri, Jan 06, 2023 at 01:53:37PM +0000, Corentin Labbe wrote:
> The CH348 is an USB octo port serial adapter.
> The device multiplexes all 8 ports in the same pair of Bulk endpoints.
> Since there is no public datasheet, unfortunately it remains some magic values
> 
> Signed-off-by: Corentin Labbe <clabbe@xxxxxxxxxxxx>
> ---
>  drivers/usb/serial/Kconfig  |   9 +
>  drivers/usb/serial/Makefile |   1 +
>  drivers/usb/serial/ch348.c  | 660 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 670 insertions(+)
>  create mode 100644 drivers/usb/serial/ch348.c
> 
> diff --git a/drivers/usb/serial/Kconfig b/drivers/usb/serial/Kconfig
> index ef8d1c73c754..1e1842656b54 100644
> --- a/drivers/usb/serial/Kconfig
> +++ b/drivers/usb/serial/Kconfig
> @@ -112,6 +112,15 @@ config USB_SERIAL_CH341
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called ch341.
>  
> +config USB_SERIAL_CH348
> +	tristate "USB Winchiphead CH348 Octo Port Serial Driver"
> +	help
> +	  Say Y here if you want to use a Winchiphead CH348 octo port
> +	  USB to serial adapter.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called ch348.
> +
>  config USB_SERIAL_WHITEHEAT
>  	tristate "USB ConnectTech WhiteHEAT Serial Driver"
>  	select USB_EZUSB_FX2
> diff --git a/drivers/usb/serial/Makefile b/drivers/usb/serial/Makefile
> index c7bb1a88173e..d16ff59fde68 100644
> --- a/drivers/usb/serial/Makefile
> +++ b/drivers/usb/serial/Makefile
> @@ -15,6 +15,7 @@ obj-$(CONFIG_USB_SERIAL_AIRCABLE)		+= aircable.o
>  obj-$(CONFIG_USB_SERIAL_ARK3116)		+= ark3116.o
>  obj-$(CONFIG_USB_SERIAL_BELKIN)			+= belkin_sa.o
>  obj-$(CONFIG_USB_SERIAL_CH341)			+= ch341.o
> +obj-$(CONFIG_USB_SERIAL_CH348)			+= ch348.o
>  obj-$(CONFIG_USB_SERIAL_CP210X)			+= cp210x.o
>  obj-$(CONFIG_USB_SERIAL_CYBERJACK)		+= cyberjack.o
>  obj-$(CONFIG_USB_SERIAL_CYPRESS_M8)		+= cypress_m8.o
> diff --git a/drivers/usb/serial/ch348.c b/drivers/usb/serial/ch348.c
> new file mode 100644
> index 000000000000..c02f403cf439
> --- /dev/null
> +++ b/drivers/usb/serial/ch348.c
> @@ -0,0 +1,660 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * USB serial driver for USB to Octal UARTs chip ch348.
> + *
> + * Copyright (C) 2022 Corentin Labbe <clabbe@xxxxxxxxxxxx>
> + * With the help of Neil Armstrong <neil.armstrong@xxxxxxxxxx>
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/serial.h>
> +#include <linux/slab.h>
> +#include <linux/tty.h>
> +#include <linux/tty_driver.h>
> +#include <linux/tty_flip.h>
> +#include <linux/usb.h>
> +#include <linux/usb/serial.h>
> +
> +#define DEFAULT_BAUD_RATE 9600
> +#define DEFAULT_TIMEOUT   2000

CH348_CMD_TIMEOUT would be more descriptive

> +
> +#define CH348_CTO_D	0x01
> +#define CH348_CTO_R	0x02
> +
> +#define CH348_CTI_C	0x10
> +#define CH348_CTI_DSR	0x20
> +#define CH348_CTI_R	0x40
> +#define CH348_CTI_DCD	0x80
> +
> +#define CH348_LO	0x02
> +#define CH348_LP	0x04
> +#define CH348_LF	0x08
> +#define CH348_LB	0x10
> +
> +#define CMD_W_R		0xC0
> +#define CMD_W_BR	0x80
> +
> +#define CMD_WB_E	0x90
> +#define CMD_RB_E	0xC0
> +
> +#define M_NOR		0x00
> +#define M_HF		0x03
> +
> +#define R_MOD		0x97
> +#define R_IO_D		0x98
> +#define R_IO_O		0x99
> +#define R_IO_I		0x9b
> +#define R_TM_O		0x9c
> +#define R_INIT		0xa1
> +
> +#define R_C1		0x01
> +#define R_C2		0x02
> +#define R_C4		0x04
> +#define R_C5		0x06
> +
> +#define R_II_B1		0x06
> +#define R_II_B2		0x02
> +#define R_II_B3		0x00
> +
> +#define CH348_RX_PORT_CHUNK_LENGTH	32
> +#define CH348_RX_PORT_MAX_LENGTH	30
> +
> +struct ch348_rxbuf {
> +	u8 port;
> +	u8 length;
> +	u8 data[CH348_RX_PORT_MAX_LENGTH];
> +} __packed;
> +
> +struct ch348_txbuf {
> +	u8 port;
> +	__le16 length;
> +	u8 data[];
> +} __packed;
> +
> +#define CH348_TX_HDRSIZE offsetof(struct ch348_txbuf, data)
> +
> +struct ch348_initbuf {
> +	u8 cmd;
> +	u8 reg;
> +	u8 port;
> +	__be32 baudrate;
> +	u8 format;
> +	u8 paritytype;
> +	u8 databits;
> +	u8 rate;
> +	u8 unk;

Please use a more descriptive name here. Is this supposed to mean
'unknown'?

> +} __packed;
> +
> +#define CH348_MAXPORT 8
> +
> +/*
> + * The CH348 multiplexes rx & tx into a pair of Bulk USB endpoints for
> + * the 8 serial ports, and another pair of Bulk USB endpoints to
> + * set port settings and receive port status events.
> + *
> + * The USB serial cores ties every Bulk endpoints pairs to each ports,
> + * but in our case it will set port 0 with the rx/tx endpoints
> + * and port 1 with the setup/status endpoints.
> + *
> + * To still take advantage of the generic code, we (re-)initialize
> + * the USB serial port structure with the correct USB endpoint
> + * for read and write, and write proper process_read_urb()
> + * and prepare_write_buffer() to correctly (de-)multiplex data.
> + */
> +
> +/**
> + * struct ch348_ttyport - per-port information
> + * @uartmode:		UART port current mode
> + * @io_status:		last reported I/O state
> + * @modem_status:	last reported modem signals state
> + */
> +struct ch348_ttyport {

Please use a less ambiguous name here as we already have tty ports.

Perhaps just 'ch348_port'?

> +	u8 uartmode;
> +	unsigned int io_status;
> +	unsigned int modem_status;
> +};
> +
> +/**
> + * struct ch348 - main container for all this driver information
> + * @udev:		pointer to the CH348 USB device
> + * @ttyport:		List of per-port information
> + * @serial:		pointer to the serial structure
> + * @rx_endpoint:	endpoint number for read operations
> + * @tx_endpoint:	endpoint number for write operations
> + * @statusrx_endpoint:	endpoint number for status operations
> + * @cmdtx_endpoint:	endpoint number for configure operations
> + * @status_read_urb:	URB for status
> + * @status_read_buffer:	buffer used by status_read_urb
> + * @status_lock:	control access of io_status/modem_status
> + * @readsize:		packet size for bulk_in
> + * @writesize:		packet size for bulk_out
> + */
> +struct ch348 {
> +	struct usb_device *udev;
> +	struct ch348_ttyport ttyport[CH348_MAXPORT];

And rename this one as well, simply 'ports'?

> +	struct usb_serial *serial;
> +
> +	int rx_endpoint;
> +	int tx_endpoint;
> +	int statusrx_endpoint;
> +	int cmdtx_endpoint;

Perhaps more readable if you use the established 'ep' for endpoint.

And the 'rx' and 'tx' infixes seem redundant, 'status_ep' and 'cmd_ep'
should do just fine.

> +
> +	struct urb *status_read_urb;
> +	u8 *status_read_buffer;

Similarly, drop '_read' here too.

> +
> +	spinlock_t status_lock;

Just 'lock'?

> +	int readsize;
> +	int writesize;
> +};
> +
> +struct ch348_magic {
> +	u8 action;
> +	u8 reg;
> +	u8 control;
> +} __packed;
> +
> +/* Some values came from vendor tree, and we have no meaning for them, this
> + * function simply use them.
> + */

Comment style is

	/*
	 * ...
	 */

Please check throughout.

> +static int ch348_do_magic(struct ch348 *ch348, int portnum, u8 action, u8 reg, u8 control)
> +{
> +	int ret = 0, len;

No need to initialise ret, and move this line after the longer struct
declaration.

> +	struct ch348_magic *buffer;
> +
> +	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> +	if (!buffer)
> +		return -ENOMEM;
> +
> +	if (portnum < 4)
> +		reg += 0x10 * portnum;
> +	else
> +		reg += 0x10 * (portnum - 4) + 0x08;
> +
> +	buffer->action = action;
> +	buffer->reg = reg;
> +	buffer->control = control;
> +
> +	ret = usb_bulk_msg(ch348->udev, ch348->cmdtx_endpoint, buffer, 3, &len,
> +			   DEFAULT_TIMEOUT);
> +	if (ret)
> +		dev_err(&ch348->udev->dev, "%s usb_bulk_msg err=%d\n", __func__, ret);

I believe I already asked you to drop __func__ from error messages and
instead spell out what went wrong, for example

	"failed to write magic: %d\n"

Please use that format consistently throughout.

> +
> +	kfree(buffer);

Newline?

> +	return ret;
> +}
> +
> +static int ch348_configure(struct ch348 *ch348, int portnum)
> +{
> +	int ret;
> +
> +	ret = ch348_do_magic(ch348, portnum, CMD_W_R, R_C2, 0x87);
> +	if (ret)
> +		return ret;

A newline seems in place here too.

> +	return ch348_do_magic(ch348, portnum, CMD_W_R, R_C4, 0x08);
> +}
> +
> +static void ch348_process_read_urb(struct urb *urb)
> +{
> +	struct usb_serial_port *port = urb->context;
> +	struct ch348 *ch348 = usb_get_serial_data(port->serial);
> +	u8 *buffer = urb->transfer_buffer, *end;

Don't mix initialisation and multiple declarations like this.

> +	unsigned int portnum, usblen;
> +	struct ch348_rxbuf *rxb;
> +
> +	if (urb->actual_length < 2) {
> +		dev_dbg(&port->dev, "%s:%d empty rx buffer\n", __func__, __LINE__);

I'm sure I've asked you drop __LINE__. Please be more careful when
considering review comments.

I'll stop doing detailed review here so you can go back and make sure
that you've addressed things I've already pointed out in previous
revisions.

Just some higher-level comments below.

> +		return;
> +	}
> +
> +	end = buffer + urb->actual_length;
> +
> +	for (; buffer < end; buffer += CH348_RX_PORT_CHUNK_LENGTH) {
> +		rxb = (struct ch348_rxbuf *)buffer;
> +		portnum = rxb->port;
> +		if (portnum >= CH348_MAXPORT) {
> +			dev_dbg(&port->dev, "%s:%d invalid port %d\n",
> +				 __func__, __LINE__, portnum);
> +			break;
> +		}
> +
> +		port = ch348->serial->port[portnum];
> +
> +		usblen = rxb->length;
> +		if (usblen > CH348_RX_PORT_MAX_LENGTH) {
> +			dev_dbg(&port->dev, "%s:%d invalid length %d for port %d\n",
> +				 __func__, __LINE__, usblen, portnum);
> +			break;
> +		}
> +
> +		tty_insert_flip_string(&port->port, rxb->data, usblen);
> +		tty_flip_buffer_push(&port->port);
> +		port->icount.rx += usblen;
> +		usb_serial_debug_data(&port->dev, __func__, usblen, rxb->data);
> +	}
> +}
> +
> +static int ch348_prepare_write_buffer(struct usb_serial_port *port, void *dest, size_t size)
> +{
> +	struct ch348_txbuf *rxt = dest;
> +	int count;
> +
> +	count = kfifo_out_locked(&port->write_fifo, rxt->data,
> +				 size - CH348_TX_HDRSIZE, &port->lock);
> +
> +	rxt->port = port->port_number;
> +	rxt->length = cpu_to_le16(count);
> +
> +	return count + CH348_TX_HDRSIZE;
> +}
> +
> +static int ch348_set_uartmode(struct ch348 *ch348, int portnum, u8 index, u8 mode)
> +{
> +	int ret;
> +
> +	if (ch348->ttyport[portnum].uartmode == M_NOR && mode == M_HF) {
> +		ret = ch348_do_magic(ch348, portnum, CMD_W_BR, R_C4, 0x51);
> +		if (ret)
> +			return ret;
> +		ch348->ttyport[portnum].uartmode = M_HF;
> +	}
> +
> +	if (ch348->ttyport[portnum].uartmode == M_HF && mode == M_NOR) {
> +		ret = ch348_do_magic(ch348, portnum, CMD_W_BR, R_C4, 0x50);
> +		if (ret)
> +			return ret;
> +		ch348->ttyport[portnum].uartmode = M_NOR;
> +	}
> +	return 0;
> +}
> +
> +static void ch348_set_termios(struct tty_struct *tty, struct usb_serial_port *port,
> +			      const struct ktermios *termios_old)
> +{
> +	struct ch348 *ch348 = usb_get_serial_data(port->serial);
> +	int portnum = port->port_number;
> +	struct ktermios *termios = &tty->termios;
> +	int ret, sent;
> +	speed_t	baudrate;
> +	u8 format;
> +	struct ch348_initbuf *buffer;
> +
> +	if (termios_old && !tty_termios_hw_change(&tty->termios, termios_old))
> +		return;
> +
> +	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> +	if (!buffer) {
> +		if (termios_old)
> +			tty->termios = *termios_old;
> +		return;
> +	}
> +
> +	baudrate = tty_get_baud_rate(tty);
> +	/* test show no success on low baud and datasheet said it is not supported */
> +	if (baudrate < 1200)
> +		baudrate = DEFAULT_BAUD_RATE;
> +	/* datasheet said it is not supported */
> +	if (baudrate > 6000000)
> +		baudrate = 6000000;
> +
> +	format = termios->c_cflag & CSTOPB ? 2 : 1;
> +
> +	buffer->paritytype = 0;
> +	if (termios->c_cflag & PARENB) {
> +		if (termios->c_cflag & PARODD)
> +			buffer->paritytype += 1;
> +		else
> +			buffer->paritytype += 2;
> +		if  (termios->c_cflag & CMSPAR)
> +			buffer->paritytype += 2;
> +	}
> +
> +	switch (C_CSIZE(tty)) {
> +	case CS5:
> +		buffer->databits = 5;
> +		break;
> +	case CS6:
> +		buffer->databits = 6;
> +		break;
> +	case CS7:
> +		buffer->databits = 7;
> +		break;
> +	case CS8:
> +	default:
> +		buffer->databits = 8;
> +		break;
> +	}
> +	buffer->cmd = CMD_WB_E | (portnum & 0x0F);
> +	buffer->reg = R_INIT;
> +	buffer->port = portnum;
> +	buffer->baudrate = cpu_to_be32(baudrate);
> +
> +	if (format == 2)
> +		buffer->format = 0x02;
> +	else if (format == 1)
> +		buffer->format = 0x00;
> +
> +	buffer->rate = max_t(speed_t, 5, DIV_ROUND_CLOSEST(10000 * 15, baudrate));
> +
> +	ret = usb_bulk_msg(ch348->udev, ch348->cmdtx_endpoint, buffer,
> +			   sizeof(*buffer), &sent, DEFAULT_TIMEOUT);
> +	if (ret < 0) {
> +		dev_err(&ch348->udev->dev, "failed to change line settings: %d\n",
> +			ret);
> +		goto out;
> +	}
> +
> +	ret = ch348_do_magic(ch348, portnum, CMD_W_R, R_C1, 0x0F);
> +	if (ret < 0)
> +		goto out;
> +
> +	if (C_CRTSCTS(tty))
> +		ret = ch348_set_uartmode(ch348, portnum, portnum, M_HF);
> +	else
> +		ret = ch348_set_uartmode(ch348, portnum, portnum, M_NOR);
> +
> +out:
> +	kfree(buffer);
> +}
> +
> +static int ch348_open(struct tty_struct *tty, struct usb_serial_port *port)
> +{
> +	struct ch348 *ch348 = usb_get_serial_data(port->serial);
> +	int ret;
> +
> +	if (tty)
> +		ch348_set_termios(tty, port, NULL);
> +
> +	ret = ch348_configure(ch348, port->port_number);
> +	if (ret) {
> +		dev_err(&ch348->udev->dev, "%s configure err\n", __func__);
> +		return ret;
> +	}
> +
> +	return usb_serial_generic_open(tty, port);
> +}
> +
> +static void ch348_update_io_status(struct ch348 *ch348, unsigned int portnum, u8 data)
> +{
> +	u8 diff;
> +
> +	if (portnum >= CH348_MAXPORT)
> +		return;
> +
> +	data &= (CH348_LO | CH348_LP | CH348_LF | CH348_LB);
> +
> +	spin_lock(&ch348->status_lock);
> +	diff = data ^ ch348->ttyport[portnum].io_status;
> +	ch348->ttyport[portnum].io_status = data;
> +	spin_unlock(&ch348->status_lock);
> +
> +	if (!diff)
> +		return;
> +
> +	if (diff & CH348_LO)
> +		ch348->serial->port[portnum]->icount.overrun++;
> +	if (diff & CH348_LP)
> +		ch348->serial->port[portnum]->icount.parity++;
> +	if (diff & CH348_LF)
> +		ch348->serial->port[portnum]->icount.frame++;
> +	if (diff & CH348_LB)
> +		ch348->serial->port[portnum]->icount.brk++;
> +
> +	wake_up_interruptible(&ch348->serial->port[portnum]->port.delta_msr_wait);
> +}
> +
> +static void ch348_update_modem_status(struct ch348 *ch348, unsigned int portnum, u8 data)
> +{
> +	struct tty_struct *tty;
> +	u8 diff;
> +
> +	if (portnum >= CH348_MAXPORT)
> +		return;
> +
> +	data &= (CH348_CTI_C | CH348_CTI_DSR | CH348_CTI_R | CH348_CTI_DCD);
> +
> +	spin_lock(&ch348->status_lock);
> +	diff = data ^ ch348->ttyport[portnum].modem_status;
> +	ch348->ttyport[portnum].modem_status = data;
> +	spin_unlock(&ch348->status_lock);
> +
> +	if (!diff)
> +		return;
> +
> +	if (diff & CH348_CTI_C)
> +		ch348->serial->port[portnum]->icount.cts++;
> +	if (diff & CH348_CTI_DSR)
> +		ch348->serial->port[portnum]->icount.dsr++;
> +	if (diff & CH348_CTI_R)
> +		ch348->serial->port[portnum]->icount.rng++;
> +	if (diff & CH348_CTI_DCD) {
> +		ch348->serial->port[portnum]->icount.dcd++;
> +
> +		tty = tty_port_tty_get(&ch348->serial->port[portnum]->port);
> +		if (tty) {
> +			usb_serial_handle_dcd_change(ch348->serial->port[portnum], tty,
> +						     data & CH348_CTI_DCD);
> +			tty_kref_put(tty);
> +		}
> +	}
> +
> +	wake_up_interruptible(&ch348->serial->port[portnum]->port.delta_msr_wait);
> +}
> +
> +static void ch348_update_status(struct ch348 *ch348, u8 *data, unsigned int len)
> +{
> +	u8 *end = data + len;
> +	unsigned int portnum, reg;
> +
> +	for (; data + 1 < end; ) {
> +		portnum = data[0] & 0xf;
> +		reg = data[1];
> +
> +		if (reg == R_INIT) {
> +			data += sizeof(struct ch348_initbuf);
> +			continue;
> +		}
> +
> +		if (reg >= R_MOD && reg <= R_IO_I) {
> +			/* This signal is used by vendor driver to handle GPIO Interrupts */
> +			dev_dbg(&ch348->udev->dev, "port%d: unhandled status %02x%02x\n",
> +				portnum, data[2], data[3]);
> +			data += 4;
> +			continue;
> +		}
> +
> +		if ((reg & 0xf) == R_II_B1) {
> +			dev_dbg(&ch348->udev->dev, "port%d: uart io state %02x\n",
> +				portnum, data[2]);
> +			ch348_update_io_status(ch348, portnum, data[2]);
> +			data += 3;
> +			continue;
> +		}
> +
> +		if ((reg & 0xf) == R_II_B2) {
> +			/* This signal is used by vendor driver to aggregate multiple port TX */
> +			dev_dbg(&ch348->udev->dev,
> +				"port%d: unhandled Write Empty status\n", portnum);
> +			data += 3;
> +			continue;
> +		}
> +
> +		if ((reg & 0xf) == R_II_B3) {
> +			dev_dbg(&ch348->udev->dev, "port%d: modem status %02x\n", portnum, data[2]);
> +			ch348_update_modem_status(ch348, portnum, data[2]);
> +			data += 3;
> +			continue;
> +		}
> +
> +		dev_dbg(&ch348->udev->dev, "port%d: unknown status %02x\n", portnum, reg);
> +		data += 3;
> +	}
> +}
> +
> +static void ch348_status_read_bulk_callback(struct urb *urb)
> +{
> +	struct ch348 *ch348 = urb->context;
> +	u8 *data = urb->transfer_buffer;
> +	unsigned int len = urb->actual_length;
> +	int ret;
> +
> +	switch (urb->status) {
> +	case 0:
> +		/* success */
> +		break;
> +	case -ECONNRESET:
> +	case -ENOENT:
> +	case -ESHUTDOWN:
> +		/* this urb is terminated, clean up */
> +		dev_dbg(&ch348->udev->dev, "%s - urb shutting down: %d\n",
> +			__func__, urb->status);
> +		return;
> +	default:
> +		dev_dbg(&ch348->udev->dev, "%s - nonzero urb status: %d\n",
> +			__func__, urb->status);
> +		goto exit;
> +	}
> +
> +	usb_serial_debug_data(&ch348->udev->dev, __func__, len, data);
> +	ch348_update_status(ch348, data, len);
> +
> +exit:
> +	ret = usb_submit_urb(urb, GFP_ATOMIC);
> +	if (ret) {
> +		dev_err(&ch348->udev->dev, "%s - failed to submit status urb: %d\n",
> +			__func__, ret);
> +	}
> +}
> +
> +static int ch348_allocate_status_read(struct ch348 *ch348, struct usb_endpoint_descriptor *epd)
> +{
> +	int buffer_size = usb_endpoint_maxp(epd);
> +
> +	ch348->status_read_urb = usb_alloc_urb(0, GFP_KERNEL);
> +	if (!ch348->status_read_urb)
> +		return -ENOMEM;
> +	ch348->status_read_buffer = kmalloc(buffer_size, GFP_KERNEL);
> +	if (!ch348->status_read_buffer) {
> +		usb_free_urb(ch348->status_read_urb);
> +		return -ENOMEM;
> +	}
> +
> +	usb_fill_bulk_urb(ch348->status_read_urb, ch348->udev,
> +			  ch348->statusrx_endpoint, ch348->status_read_buffer,
> +			  buffer_size, ch348_status_read_bulk_callback, ch348);
> +
> +	return 0;
> +}
> +
> +static void ch348_release(struct usb_serial *serial)
> +{
> +	struct ch348 *ch348 = usb_get_serial_data(serial);
> +
> +	usb_kill_urb(ch348->status_read_urb);
> +	usb_free_urb(ch348->status_read_urb);
> +	kfree(ch348->status_read_buffer);
> +}

You need to implement disconnect() as well if you are to manage the
status URB like this as stopping when the last tty reference is closed
is too late.

But should instead handle the status urb like mxuport does, but using
port1 for status events and starting it at attach or when the first port
is opened.

> +
> +static int ch348_probe(struct usb_serial *serial, const struct usb_device_id *id)
> +{
> +	struct usb_interface *intf;
> +	struct usb_endpoint_descriptor *epcmdwrite = NULL;
> +	struct usb_endpoint_descriptor *epstatusread = NULL;
> +	struct usb_endpoint_descriptor *epread = NULL;
> +	struct usb_endpoint_descriptor *epwrite = NULL;

No need to initialise.

> +	struct usb_device *usb_dev = serial->dev;
> +	struct ch348 *ch348;
> +	int ret;
> +
> +	intf = usb_ifnum_to_if(usb_dev, 0);
> +
> +	ret = usb_find_common_endpoints(intf->cur_altsetting, &epread, &epwrite,
> +					NULL, NULL);
> +	if (ret) {
> +		dev_err(&serial->dev->dev, "ERROR: failed to find basic endpoints ret=%d\n", ret);
> +		return ret;
> +	}

You should not need the above as core will take care of allocating the
bulk urbs and buffers.

> +	epstatusread = &intf->cur_altsetting->endpoint[2].desc;
> +	epcmdwrite = &intf->cur_altsetting->endpoint[3].desc;

You need to check that you actually have four endpoints before using
these pointers.

This can also be done by setting num_bulk_in and num_bulk_out in the
usb_serial_driver structure below.

> +
> +	if (!usb_endpoint_is_bulk_in(epstatusread)) {
> +		dev_err(&serial->dev->dev, "ERROR: missing second bulk in\n");
> +		return -EINVAL;
> +	}
> +	if (!usb_endpoint_is_bulk_out(epcmdwrite)) {
> +		dev_err(&serial->dev->dev, "ERROR: missing second bulk out\n");
> +		return -EINVAL;
> +	}
> +
> +	ch348 = devm_kzalloc(&serial->dev->dev, sizeof(*ch348), GFP_KERNEL);

You cannot use devres here (or in general for drivers exposing a
chardev), these structures may need to stay around after the device has
been disconnected as user space can still hold a reference to the tty.

You'd currently trigger a use-after-free in release() above when trying
to access the driver data which would already have been freed in case
user space holds the tty open longer.

Also allocations should be done in an attach() callback which matches
release() (so this function should be converted to an attach()
callback).

> +	if (!ch348)
> +		return -ENOMEM;
> +
> +	usb_set_serial_data(serial, ch348);
> +
> +	ch348->readsize = usb_endpoint_maxp(epread);
> +	ch348->writesize = usb_endpoint_maxp(epwrite);

These are in fact not even used anymore...

> +	ch348->udev = serial->dev;
> +	ch348->serial = serial;
> +
> +	spin_lock_init(&ch348->status_lock);
> +
> +	ch348->rx_endpoint = usb_rcvbulkpipe(usb_dev, epread->bEndpointAddress);
> +	ch348->tx_endpoint = usb_sndbulkpipe(usb_dev, epwrite->bEndpointAddress);

These are also no longer used.

> +	ch348->cmdtx_endpoint = usb_sndbulkpipe(usb_dev, epcmdwrite->bEndpointAddress);
> +	ch348->statusrx_endpoint = usb_rcvbulkpipe(usb_dev, epstatusread->bEndpointAddress);
> +
> +	ret = ch348_allocate_status_read(ch348, epstatusread);
> +	if (ret)
> +		return ret;
> +	return 0;
> +}
> +
> +static int ch348_calc_num_ports(struct usb_serial *serial,
> +				struct usb_serial_endpoints *epds)
> +{
> +	int i;
> +
> +	for (i = 1; i < CH348_MAXPORT; ++i) {
> +		epds->bulk_out[i] = epds->bulk_out[0];
> +		epds->bulk_in[i] = epds->bulk_in[0];

So as I mentioned above, try following the mxuport pattern here also for
the bulk_in endpoints and use port0 and port1 respectively for reading
data and events.

> +	}
> +	epds->num_bulk_out = CH348_MAXPORT;
> +	epds->num_bulk_in = CH348_MAXPORT;

Newline.

> +	return CH348_MAXPORT;
> +}
> +
> +static const struct usb_device_id ch348_ids[] = {
> +	{ USB_DEVICE(0x1a86, 0x55d9), },
> +	{ }
> +};
> +
> +MODULE_DEVICE_TABLE(usb, ch348_ids);
> +
> +static struct usb_serial_driver ch348_device = {
> +	.driver = {
> +		.owner = THIS_MODULE,
> +		.name = "ch348",
> +	},
> +	.id_table =		ch348_ids,
> +	.num_ports =		CH348_MAXPORT,
> +	.open =			ch348_open,
> +	.set_termios =		ch348_set_termios,
> +	.process_read_urb =	ch348_process_read_urb,
> +	.prepare_write_buffer =	ch348_prepare_write_buffer,
> +	.probe =		ch348_probe,
> +	.calc_num_ports =	ch348_calc_num_ports,
> +	.release =		ch348_release,
> +};
> +
> +static struct usb_serial_driver * const serial_drivers[] = {
> +	&ch348_device, NULL
> +};
> +
> +module_usb_serial_driver(serial_drivers, ch348_ids);
> +
> +MODULE_AUTHOR("Corentin Labbe <clabbe@xxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("USB CH348 Octo port serial converter driver");
> +MODULE_LICENSE("GPL");

Johan