Re: [PATCH v3 1/2] usb: serial: Add MaxLinear/Exar USB to Serial driver

[Manivannan Sadhasivam <mani@kernel.org>]

Hi Johan,

Thanks for the review. Please find the replies inline.

On Tue, May 19, 2020 at 02:33:38PM +0200, Johan Hovold wrote:
> On Fri, May 01, 2020 at 12:19:23AM +0530, mani@kernel.org wrote:
> > From: Manivannan Sadhasivam <mani@kernel.org>
> > 
> > Add support for MaxLinear/Exar USB to Serial converters. This driver
> > only supports XR21V141X series but it can be extended to other series
> > from Exar as well in future.
> > 
> > This driver is inspired from the initial one submitted by Patong Yang:
> > 
> > https://patchwork.kernel.org/patch/10543261/
> > 
> > While the initial driver was a custom tty USB driver exposing whole
> > new serial interface ttyXRUSBn, this version is completely based on USB
> > serial core thus exposing the interfaces as ttyUSBn. This will avoid
> > the overhead of exposing a new USB serial interface which the userspace
> > tools are unaware of.
> > 
> > Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
> > ---
> >  drivers/usb/serial/Kconfig     |   9 +
> >  drivers/usb/serial/Makefile    |   1 +
> >  drivers/usb/serial/xr_serial.c | 624 +++++++++++++++++++++++++++++++++
> >  3 files changed, 634 insertions(+)
> >  create mode 100644 drivers/usb/serial/xr_serial.c
> > 
> > diff --git a/drivers/usb/serial/Kconfig b/drivers/usb/serial/Kconfig
> > index 25d7e0c36d38..8f6ad9f94735 100644
> > --- a/drivers/usb/serial/Kconfig
> > +++ b/drivers/usb/serial/Kconfig
> > @@ -644,6 +644,15 @@ config USB_SERIAL_UPD78F0730
> >  	  To compile this driver as a module, choose M here: the
> >  	  module will be called upd78f0730.
> >  
> > +config USB_SERIAL_XR
> > +	tristate "USB MaxLinear/Exar USB to Serial driver"
> > +	help
> > +	  Say Y here if you want to use MaxLinear/Exar USB to Serial converter
> > +	  devices.
> > +
> > +	  To compile this driver as a module, choose M here: the
> > +	  module will be called xr_serial.
> > +
> >  config USB_SERIAL_DEBUG
> >  	tristate "USB Debugging Device"
> >  	help
> > diff --git a/drivers/usb/serial/Makefile b/drivers/usb/serial/Makefile
> > index 2d491e434f11..4f69c2a3aff3 100644
> > --- a/drivers/usb/serial/Makefile
> > +++ b/drivers/usb/serial/Makefile
> > @@ -62,4 +62,5 @@ obj-$(CONFIG_USB_SERIAL_VISOR)			+= visor.o
> >  obj-$(CONFIG_USB_SERIAL_WISHBONE)		+= wishbone-serial.o
> >  obj-$(CONFIG_USB_SERIAL_WHITEHEAT)		+= whiteheat.o
> >  obj-$(CONFIG_USB_SERIAL_XIRCOM)			+= keyspan_pda.o
> > +obj-$(CONFIG_USB_SERIAL_XR)			+= xr_serial.o
> >  obj-$(CONFIG_USB_SERIAL_XSENS_MT)		+= xsens_mt.o
> > diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
> > new file mode 100644
> > index 000000000000..fdb9ddf8bd95
> > --- /dev/null
> > +++ b/drivers/usb/serial/xr_serial.c
> > @@ -0,0 +1,624 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * MaxLinear/Exar USB to Serial driver
> > + *
> > + * Based on initial driver written by Patong Yang <patong.mxl@gmail.com>
> > + *
> > + * Copyright (c) 2020 Manivannan Sadhasivam <mani@kernel.org>
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/slab.h>
> > +#include <linux/tty.h>
> > +#include <linux/usb.h>
> > +#include <linux/usb/serial.h>
> > +
> > +struct xr_uart_regs {
> > +	u8 enable;
> > +	u8 format;
> > +	u8 flow_ctrl;
> > +	u8 xon_char;
> > +	u8 xoff_char;
> > +	u8 loopback;
> > +	u8 tx_break;
> > +	u8 rs485_delay;
> > +	u8 gpio_mode;
> > +	u8 gpio_dir;
> > +	u8 gpio_int_mask;
> > +	u8 gpio_set;
> > +	u8 gpio_clr;
> > +	u8 gpio_status;
> > +};
> > +
> > +struct xr_port_private {
> > +	const struct xr_uart_regs *regs;
> > +};
> > +
> > +struct xr_txrx_clk_mask {
> > +	u16 tx;
> > +	u16 rx0;
> > +	u16 rx1;
> > +};
> > +
> > +#define XR21V141X_ID			0x1410
> > +#define XR_INT_OSC_HZ			48000000
> > +
> > +/* USB Requests */
> > +#define XR_SET_XR21V141X		0
> > +#define XR_GET_XR21V141X		1
> > +
> > +#define XR21V141X_CLOCK_DIVISOR_0	0x4
> > +#define XR21V141X_CLOCK_DIVISOR_1	0x5
> > +#define XR21V141X_CLOCK_DIVISOR_2	0x6
> > +#define XR21V141X_TX_CLOCK_MASK_0	0x7
> > +#define XR21V141X_TX_CLOCK_MASK_1	0x8
> > +#define XR21V141X_RX_CLOCK_MASK_0	0x9
> > +#define XR21V141X_RX_CLOCK_MASK_1	0xa
> > +
> > +/* XR21V141X register blocks */
> > +#define XR21V141X_UART_REG_BLOCK	0
> > +#define XR21V141X_URM_REG_BLOCK		4
> > +#define XR21V141X_UART_CUSTOM_BLOCK	0x66
> > +
> > +/* XR21V141X UART Manager Registers */
> > +#define XR21V141X_URM_FIFO_ENABLE_REG	0x10
> > +#define XR21V141X_URM_ENABLE_TX_FIFO	0x1
> > +#define XR21V141X_URM_ENABLE_RX_FIFO	0x2
> > +
> > +#define XR21V141X_URM_RX_FIFO_RESET	0x18
> > +#define XR21V141X_URM_TX_FIFO_RESET	0x1c
> 
> Did you mean to use "UMR" above? What does URM stand for otherwise?
> 

UART Manager. I'll just use 'UART_MANAGER' to make it more explicit.

> > +
> > +#define UART_ENABLE_TX			0x1
> > +#define UART_ENABLE_RX			0x2
> > +
> > +#define UART_MODE_RI			BIT(0)
> > +#define UART_MODE_CD			BIT(1)
> > +#define UART_MODE_DSR			BIT(2)
> > +#define UART_MODE_DTR			BIT(3)
> > +#define UART_MODE_CTS			BIT(4)
> > +#define UART_MODE_RTS			BIT(5)
> > +
> > +#define UART_BREAK_ON			0xff
> > +#define UART_BREAK_OFF			0
> > +
> > +#define UART_DATA_MASK			GENMASK(3, 0)
> > +#define UART_DATA_7			0x7
> > +#define UART_DATA_8			0x8
> > +
> > +#define UART_PARITY_MASK		GENMASK(6, 4)
> > +#define UART_PARITY_SHIFT		0x4
> > +#define UART_PARITY_NONE		0x0
> > +#define UART_PARITY_ODD			0x1
> > +#define UART_PARITY_EVEN		0x2
> > +#define UART_PARITY_MARK		0x3
> > +#define UART_PARITY_SPACE		0x4
> > +
> > +#define UART_STOP_MASK			BIT(7)
> > +#define UART_STOP_SHIFT			0x7
> > +#define UART_STOP_1			0x0
> > +#define UART_STOP_2			0x1
> > +
> > +#define UART_FLOW_MODE_NONE		0x0
> > +#define UART_FLOW_MODE_HW		0x1
> > +#define UART_FLOW_MODE_SW		0x2
> > +
> > +#define UART_MODE_GPIO			0x0
> > +#define UART_MODE_RTS_CTS		0x1
> > +#define UART_MODE_DTR_DSR		0x2
> > +#define UART_MODE_RS485			0x3
> > +#define UART_MODE_RS485_ADDR		0x4
> > +
> > +static const struct xr_uart_regs xr21v141x_regs = {
> > +	.enable = 0x03,
> > +	.format = 0x0b,
> > +	.flow_ctrl = 0x0c,
> > +	.xon_char = 0x10,
> > +	.xoff_char = 0x11,
> > +	.loopback = 0x12,
> > +	.tx_break = 0x14,
> > +	.rs485_delay = 0x15,
> > +	.gpio_mode = 0x1a,
> > +	.gpio_dir = 0x1b,
> > +	.gpio_int_mask = 0x1c,
> > +	.gpio_set = 0x1d,
> > +	.gpio_clr = 0x1e,
> > +	.gpio_status = 0x1f,
> > +};
> 
> Do you expect there to be more models supported by this driver? Perhaps
> you shouldn't add this abstraction until then.
> 

Yes, I do expect more revisions to get added in future.

> > +static int xr_set_reg(struct usb_serial_port *port, u8 block, u8 reg,
> > +		      u8 val)
> > +{
> > +	struct usb_serial *serial = port->serial;
> > +	int ret = -EINVAL;
> 
> Pointless init.
> 
> > +
> > +	/* XR21V141X uses custom command for writing UART registers */
> 
> I'd drop this comment. These control messages are also used to access
> the EEPROM etc.
> 
> > +	ret = usb_control_msg(serial->dev,
> > +			      usb_sndctrlpipe(serial->dev, 0),
> > +			      XR_SET_XR21V141X,
> > +			      USB_DIR_OUT | USB_TYPE_VENDOR, val,
> > +			      reg | (block << 8), NULL, 0,
> > +			      USB_CTRL_SET_TIMEOUT);
> > +
> 
> Remove this newline.
> 
> > +	if (ret < 0)
> > +		dev_err(&port->dev, "Failed to set reg 0x%x status: %d\n",
> 
> %02x; and skip "status" like:
> 
> 	dev_err(&port->dev, "failed to set reg 0x%02x: %d\n",
> 
> > +			reg, ret);
> > +
> > +	return ret;
> 
> As Greg suggested, please return 0 explicitly here on success.
> 
> > +}
> > +
> > +static int xr_get_reg(struct usb_serial_port *port, u8 block, u8 reg,
> > +		      u8 *val)
> > +{
> > +	struct usb_serial *serial = port->serial;
> > +	void *dmabuf;
> > +	int ret = -EINVAL;
> 
> Unnecessary, again.
> 
> > +
> > +	dmabuf = kmalloc(1, GFP_KERNEL);
> > +	if (!dmabuf)
> > +		return -ENOMEM;
> > +
> > +	/* XR21V141X uses custom command for reading UART registers */
> 
> Drop this.
> 
> > +	ret = usb_control_msg(serial->dev,
> > +			      usb_rcvctrlpipe(serial->dev, 0),
> > +			      XR_GET_XR21V141X,
> > +			      USB_DIR_IN | USB_TYPE_VENDOR, 0,
> > +			      reg | (block << 8), dmabuf, 1,
> > +			      USB_CTRL_SET_TIMEOUT);
> 
> s/SET/GET/
> 
> > +
> 
> No newline.
> 
> > +	if (ret == 1) {
> > +		memcpy(val, dmabuf, 1);
> 
> Use u8 and assignment here as Greg suggested.
> 
> > +		ret = 0;
> > +	} else {
> > +		dev_err(&port->dev, "Failed to get reg 0x%x status: %d\n",
> 
> As above.
> 
> > +			reg, ret);
> > +		if (ret >= 0)
> > +			ret = -EIO;
> > +	}
> > +
> > +	kfree(dmabuf);
> > +
> > +	return ret;
> > +}
> > +
> > +/* Tx and Rx clock mask values obtained from section 3.3.4 of datasheet */
> > +static const struct xr_txrx_clk_mask xr21v141x_txrx_clk_masks[] = {
> > +	{ 0x000, 0x000, 0x000 },
> > +	{ 0x000, 0x000, 0x000 },
> > +	{ 0x100, 0x000, 0x100 },
> > +	{ 0x020, 0x400, 0x020 },
> > +	{ 0x010, 0x100, 0x010 },
> > +	{ 0x208, 0x040, 0x208 },
> > +	{ 0x104, 0x820, 0x108 },
> > +	{ 0x844, 0x210, 0x884 },
> > +	{ 0x444, 0x110, 0x444 },
> > +	{ 0x122, 0x888, 0x224 },
> > +	{ 0x912, 0x448, 0x924 },
> > +	{ 0x492, 0x248, 0x492 },
> > +	{ 0x252, 0x928, 0x292 },
> > +	{ 0x94a, 0x4a4, 0xa52 },
> > +	{ 0x52a, 0xaa4, 0x54a },
> > +	{ 0xaaa, 0x954, 0x4aa },
> > +	{ 0xaaa, 0x554, 0xaaa },
> > +	{ 0x555, 0xad4, 0x5aa },
> > +	{ 0xb55, 0xab4, 0x55a },
> > +	{ 0x6b5, 0x5ac, 0xb56 },
> > +	{ 0x5b5, 0xd6c, 0x6d6 },
> > +	{ 0xb6d, 0xb6a, 0xdb6 },
> > +	{ 0x76d, 0x6da, 0xbb6 },
> > +	{ 0xedd, 0xdda, 0x76e },
> > +	{ 0xddd, 0xbba, 0xeee },
> > +	{ 0x7bb, 0xf7a, 0xdde },
> > +	{ 0xf7b, 0xef6, 0x7de },
> > +	{ 0xdf7, 0xbf6, 0xf7e },
> > +	{ 0x7f7, 0xfee, 0xefe },
> > +	{ 0xfdf, 0xfbe, 0x7fe },
> > +	{ 0xf7f, 0xefe, 0xffe },
> > +	{ 0xfff, 0xffe, 0xffd },
> > +};
> > +
> > +static int xr_set_baudrate(struct tty_struct *tty,
> > +			   struct usb_serial_port *port)
> > +{
> > +	u32 divisor = XR_INT_OSC_HZ / tty->termios.c_ospeed;
> 
> Boom -- division by zero. B0 should drop DTR/RTS.
> 

Ah right. Will clamp the baud rate based on min and max values.

> > +	u32 idx = (32 * divisor) & 0x1f;
> > +	u16 tx_mask = xr21v141x_txrx_clk_masks[idx].tx;
> > +	u16 rx_mask = (divisor & 1) ? xr21v141x_txrx_clk_masks[idx].rx1 :
> > +				      xr21v141x_txrx_clk_masks[idx].rx0;
> 
> Don't do non-trivial initialisations like this as part of declaration.
> Avoid the ternary operator.
> 

Okay.

> > +	int ret;
> > +
> > +	dev_dbg(&port->dev, "Setting baud rate :%u\n", tty->termios.c_ospeed);
> 
> Space after ':', not before.
> 
> > +
> > +	/*
> > +	 * XR21V141X uses fractional baud rate generator with 48MHz internal
> > +	 * oscillator and 19-bit programmable divisor. So theoretically it can
> > +	 * generate most commonly used baud rates with high accuracy.
> > +	 */
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_CLOCK_DIVISOR_0, (divisor & 0xff));
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_CLOCK_DIVISOR_1, ((divisor >>  8) & 0xff));
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_CLOCK_DIVISOR_2, ((divisor >> 16) & 0xff));
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_TX_CLOCK_MASK_0, (tx_mask & 0xff));
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_TX_CLOCK_MASK_1, ((tx_mask >>  8) & 0xff));
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_RX_CLOCK_MASK_0, (rx_mask & 0xff));
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 XR21V141X_RX_CLOCK_MASK_1, ((rx_mask >>  8) & 0xff));
> > +
> > +	return ret;
> > +}
> > +
> > +/*
> > + * According to datasheet, below is the recommended sequence for enabling UART
> > + * module in XR21V141X:
> > + *
> > + * Enable Tx FIFO
> > + * Enable Tx and Rx
> > + * Enable Rx FIFO
> > + */
> > +static int xr_uart_enable(struct usb_serial_port *port)
> > +{
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	int ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_URM_REG_BLOCK,
> > +			 XR21V141X_URM_FIFO_ENABLE_REG,
> > +			 XR21V141X_URM_ENABLE_TX_FIFO);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->enable,
> > +			 UART_ENABLE_TX | UART_ENABLE_RX);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_URM_REG_BLOCK,
> > +			 XR21V141X_URM_FIFO_ENABLE_REG,
> > +			 XR21V141X_URM_ENABLE_TX_FIFO |
> > +			 XR21V141X_URM_ENABLE_RX_FIFO);
> 
> Should you be undoing these on errors?
> 

If it happens then most probably the connection got lost. Should we still try
to set registers?

> > +
> > +	return ret;
> > +}
> > +
> > +static int xr_uart_disable(struct usb_serial_port *port)
> > +{
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	int ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->enable, 0);
> > +	if (ret)
> > +		return ret;
> > +
> > +	ret = xr_set_reg(port, XR21V141X_URM_REG_BLOCK,
> > +			 XR21V141X_URM_FIFO_ENABLE_REG, 0);
> > +
> > +	return ret;
> > +}
> > +
> > +static int xr_open(struct tty_struct *tty, struct usb_serial_port *port)
> > +{
> > +	int ret;
> > +
> > +	ret = xr_uart_enable(port);
> > +	if (ret) {
> > +		dev_err(&port->dev, "Failed to enable UART\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = xr_set_baudrate(tty, port);
> 
> tty will be NULL when called by the console driver.
> 
> Why only init the line speed? Driver typically call set_termios() here
> when not used as a console.
> 

Will fix this.

> > +	if (ret) {
> > +		dev_err(&port->dev, "Failed to set baudrate\n");
> > +		return ret;
> > +	}
> > +
> > +	return usb_serial_generic_open(tty, port);
> 
> Disable on errors?
> 

Ack.

> > +}
> > +
> > +static void xr_close(struct usb_serial_port *port)
> > +{
> > +	usb_serial_generic_close(port);
> > +
> > +	xr_uart_disable(port);
> > +}
> > +
> > +static void xr_set_flow_mode(struct tty_struct *tty,
> > +			     struct usb_serial_port *port,
> > +			     unsigned int cflag)
> > +{
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	u8 flow, gpio_mode;
> > +	int ret;
> > +
> > +	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->gpio_mode, &gpio_mode);
> > +	if (ret)
> > +		return;
> > +
> > +	if (cflag & CRTSCTS) {
> > +		dev_dbg(&port->dev, "Enabling hardware flow ctrl\n");
> > +		flow = UART_FLOW_MODE_HW;
> > +		gpio_mode |= UART_MODE_RTS_CTS;
> 
> These modes are exclusive, you cannot use |= here.
> 
> > +	} else if (I_IXOFF(tty) || I_IXON(tty)) {
> 
> This should just be IXOFF(tty) (flow control on input).
> 
> > +		u8 start_char = START_CHAR(tty);
> > +		u8 stop_char = STOP_CHAR(tty);
> > +
> > +		dev_dbg(&port->dev, "Enabling sw flow ctrl\n");
> > +		flow = UART_FLOW_MODE_SW;
> > +		gpio_mode |= UART_MODE_GPIO;
> 
> Same here, this is broken; ORing with 0 doesn't set mode 0.
> 
> > +
> > +		xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			   port_priv->regs->xon_char, start_char);
> > +		xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			   port_priv->regs->xoff_char, stop_char);
> > +	} else {
> > +		dev_dbg(&port->dev, "No flow ctrl\n");
> > +		flow = UART_FLOW_MODE_NONE;
> 
> I assume you need to set UART_MODE_GPIO here too to be able to control
> RTS manually (default mode is RTS/CTS flow control).
> 
> > +	}
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->flow_ctrl, flow);
> > +	if (ret)
> > +		return;
> 
> The datasheet says that the flow control register can only be updated
> when the uart is disabled.
> 
> 	"These registers should only be written to when the UART is
> 	 disabled. Writing to the FLOW_CONTROL register when the UART is
> 	 enabled will result in undefined behavior."
> 

Ack.

> > +
> > +	xr_set_reg(port, XR21V141X_UART_REG_BLOCK, port_priv->regs->gpio_mode,
> > +		   gpio_mode);
> > +}
> > +
> > +static void xr_set_termios(struct tty_struct *tty,
> > +			   struct usb_serial_port *port,
> > +			   struct ktermios *old_termios)
> > +{
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	struct device *dev = &port->dev;
> > +	unsigned int cflag, old_cflag;
> > +	int ret;
> > +	u8 bits;
> > +
> > +	cflag = tty->termios.c_cflag;
> > +	old_cflag = old_termios->c_cflag;
> > +
> > +	if (tty->termios.c_ospeed != old_termios->c_ospeed)
> > +		xr_set_baudrate(tty, port);
> > +
> > +	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->format, &bits);
> > +	if (ret)
> > +		return;
> 
> No need to retrieve the current settings.
> 
> > +
> > +	/* If the number of data bits is to be updated */
> > +	if ((cflag & CSIZE) != (old_cflag & CSIZE)) {
> 
> Use C_CSIZE(tty) and friends and set these unconditionally.
> 
> > +		bits &= ~UART_DATA_MASK;
> > +		switch (cflag & CSIZE) {
> > +		case CS7:
> > +			bits |= UART_DATA_7;
> > +			dev_dbg(dev, "Setting data bits: 7\n");
> > +			break;
> > +		case CS8:
> > +		/* CS9 not supported */
> > +		default:
> > +			bits |= UART_DATA_8;
> > +			dev_dbg(dev, "Setting data bits: 8\n");
> 
> You should report back that you cannot set CS5 and CS6 by restoring the
> old setting in tty->termios.
> 

Okay.

> > +			break;
> > +		}
> > +	}
> > +
> > +	if ((cflag & (PARENB | PARODD | CMSPAR)) !=
> > +	    (old_cflag & (PARENB | PARODD | CMSPAR))) {
> 
> As above, determine these bits unconditionally.
> 
> > +		bits &= ~UART_PARITY_MASK;
> > +		if (cflag & PARENB) {
> > +			if (cflag & CMSPAR) {
> > +				if (cflag & PARODD) {
> > +					bits |= (UART_PARITY_MARK <<
> > +						 UART_PARITY_SHIFT);
> 
> Parenthesis not need. Hopefully cleaner when you have reduced
> indentation.
> 
> > +					dev_dbg(dev, "Setting parity: MARK\n");
> > +				} else {
> > +					bits |= (UART_PARITY_SPACE <<
> > +						 UART_PARITY_SHIFT);
> > +					dev_dbg(dev, "Setting parity: SPACE\n");
> > +				}
> > +			} else {
> > +				if (cflag & PARODD) {
> > +					bits |= (UART_PARITY_ODD <<
> > +						 UART_PARITY_SHIFT);
> > +					dev_dbg(dev, "Setting parity: ODD\n");
> > +				} else {
> > +					bits |= (UART_PARITY_EVEN <<
> > +						 UART_PARITY_SHIFT);
> > +					dev_dbg(dev, "Setting parity: EVEN\n");
> 
> And please drop all these dev_dbg (also for data bits).
> 
> > +				}
> > +			}
> > +		}
> > +	}
> > +
> > +	if ((cflag & CSTOPB) != (old_cflag & CSTOPB)) {
> > +		bits &= ~UART_STOP_MASK;
> > +		if (cflag & CSTOPB) {
> > +			bits |= (UART_STOP_2 << UART_STOP_SHIFT);
> > +			dev_dbg(dev, "Setting stop bits: 2\n");
> > +		} else {
> > +			bits |= (UART_STOP_1 << UART_STOP_SHIFT);
> > +			dev_dbg(dev, "Setting stop bits: 1\n");
> > +		}
> > +	}
> 
> As above.
> 
> > +
> > +	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->format, (bits & 0xff));
> 
> bits is u8, no need to mask
> 
> > +	if (ret)
> > +		return;
> > +
> > +	xr_set_flow_mode(tty, port, cflag);
> 
> cflag can be retreived from tty.
> 

Ack.

> > +}
> > +
> > +static int xr_tiocmset_port(struct usb_serial_port *port,
> > +			    unsigned int set, unsigned int clear)
> > +{
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	int ret = 0;
> > +	u8 gpio_set = 0;
> > +	u8 gpio_clr = 0;
> > +
> > +	/* Modem control pins are active low, so set & clr are swapped */
> > +	if (set & TIOCM_RTS)
> > +		gpio_clr |= UART_MODE_RTS;
> > +	if (set & TIOCM_DTR)
> > +		gpio_clr |= UART_MODE_DTR;
> > +	if (clear & TIOCM_RTS)
> > +		gpio_set |= UART_MODE_RTS;
> > +	if (clear & TIOCM_DTR)
> > +		gpio_set |= UART_MODE_DTR;
> > +
> > +	/* Writing '0' to gpio_{set/clr} bits has no effect, so no need to do */
> > +	if (gpio_clr)
> > +		ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +				 port_priv->regs->gpio_clr, gpio_clr);
> 
> Please add brackets since you have a multiline statement here.
> 
> > +
> > +	if (gpio_set)
> > +		ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
> > +				 port_priv->regs->gpio_set, gpio_set);
> 
> Same here.
> 
> > +
> > +	return ret;
> > +}
> > +
> > +static int xr_tiocmset(struct tty_struct *tty,
> > +		       unsigned int set, unsigned int clear)
> > +{
> > +	struct usb_serial_port *port = tty->driver_data;
> > +
> > +	return xr_tiocmset_port(port, set, clear);
> > +}
> > +
> > +static void xr_dtr_rts(struct usb_serial_port *port, int on)
> > +{
> > +	if (on)
> > +		xr_tiocmset_port(port, TIOCM_DTR | TIOCM_RTS, 0);
> > +	else
> > +		xr_tiocmset_port(port, 0, TIOCM_DTR | TIOCM_RTS);
> > +}
> > +
> > +static int xr_tiocmget(struct tty_struct *tty)
> > +{
> > +	struct usb_serial_port *port = tty->driver_data;
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	int ret;
> > +	u8 status;
> > +
> > +	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
> > +			 port_priv->regs->gpio_status, &status);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/*
> > +	 * Modem control pins are active low, so reading '0' means it is active
> > +	 * and '1' means not active.
> > +	 */
> > +	ret = ((status & UART_MODE_DTR) ? 0 : TIOCM_DTR) |
> > +	      ((status & UART_MODE_RTS) ? 0 : TIOCM_RTS) |
> > +	      ((status & UART_MODE_CTS) ? 0 : TIOCM_CTS) |
> > +	      ((status & UART_MODE_DSR) ? 0 : TIOCM_DSR) |
> > +	      ((status & UART_MODE_RI) ? 0 : TIOCM_RI) |
> > +	      ((status & UART_MODE_CD) ? 0 : TIOCM_CD);
> 
> Can you read back also the outputs? Also in automatic mode?
> 

Yes I guess. The datasheet doesn't specify any limitation here afaik.

> > +
> > +	return ret;
> > +}
> > +
> > +static void xr_break_ctl(struct tty_struct *tty, int break_state)
> > +{
> > +	struct usb_serial_port *port = tty->driver_data;
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +	u8 state;
> > +
> > +	if (break_state == 0)
> > +		state = UART_BREAK_OFF;
> > +	else
> > +		state = UART_BREAK_ON;
> > +
> > +	dev_dbg(&port->dev, "Turning break %s\n",
> > +		state == UART_BREAK_OFF ? "off" : "on");
> > +	xr_set_reg(port, XR21V141X_UART_REG_BLOCK, port_priv->regs->tx_break,
> > +		   state);
> > +}
> > +
> > +static int xr_port_probe(struct usb_serial_port *port)
> > +{
> > +	struct xr_port_private *port_priv;
> > +
> > +	port_priv = kzalloc(sizeof(*port_priv), GFP_KERNEL);
> > +	if (!port_priv)
> > +		return -ENOMEM;
> > +
> > +	/* XR21V141X specific settings */
> > +	port_priv->regs = &xr21v141x_regs;
> 
> May not be needed.
> 

I'd like to keep some sort of generalism to ease adding more revisions in
future.

> > +
> > +	usb_set_serial_port_data(port, port_priv);
> > +
> > +	return 0;
> > +}
> > +
> > +static int xr_port_remove(struct usb_serial_port *port)
> > +{
> > +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> > +
> > +	kfree(port_priv);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct usb_device_id id_table[] = {
> > +	{ USB_DEVICE(0x04e2, 0x1410) }, /* XR21V141X */
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(usb, id_table);
> > +
> > +static struct usb_serial_driver xr_device = {
> > +	.driver = {
> > +		.owner = THIS_MODULE,
> > +		.name =	"xr_serial",
> > +	},
> > +	.id_table		= id_table,
> > +	.num_ports		= 1,
> > +	.bulk_in_size		= 384,
> > +	.bulk_out_size		= 128,
> 
> You should not necessarily set these to match the hardware fifo sizes.
> They default to the respective endpoint size, but may be increased for
> improved throughput.
> 

Okay.

> > +	.open			= xr_open,
> > +	.close			= xr_close,
> > +	.break_ctl		= xr_break_ctl,
> > +	.set_termios		= xr_set_termios,
> > +	.tiocmget		= xr_tiocmget,
> > +	.tiocmset		= xr_tiocmset,
> > +	.port_probe		= xr_port_probe,
> > +	.port_remove		= xr_port_remove,
> > +	.dtr_rts		= xr_dtr_rts
> > +};
> 
> As I mentioned elsewhere, you should only register a tty device for the
> data interface, but still claim the control interface.
> 
> You probably should reject the control interface and claim it when
> probing the data interface (rather than return 1 from attach as I
> mentioned earlier).
> 

This seems to be a much more cleaner solution. Will stick to it.

Thanks,
Mani

> > +
> > +static struct usb_serial_driver * const serial_drivers[] = {
> > +	&xr_device, NULL
> > +};
> > +
> > +module_usb_serial_driver(serial_drivers, id_table);
> > +
> > +MODULE_AUTHOR("Manivannan Sadhasivam <mani@kernel.org>");
> > +MODULE_DESCRIPTION("MaxLinear/Exar USB to Serial driver");
> > +MODULE_LICENSE("GPL");
> 
> Generally nice and clean overall.
> 
> Johan