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

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Apr 29, 2020 at 01:26:50AM +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 provision has been made to support
> other series 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.

Nice work!

Some comments below:

> +// 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>
> +
> +#include "xr_serial.h"

No need for a .h file for a single .c file.

> +static int xr_get_reg(struct usb_serial_port *port, u8 block, u16 reg,
> +		      u16 *val)
> +{
> +	struct usb_serial *serial = port->serial;
> +	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
> +	void *dmabuf;
> +	int ret = -EINVAL;
> +
> +	dmabuf = kmalloc(sizeof(reg), GFP_KERNEL);

So that is 2 bytes?

> +	if (!dmabuf)
> +		return -ENOMEM;
> +
> +	if (port_priv->idProduct == XR21V141X_ID) {
> +		/* XR21V141X uses custom command for reading UART registers */
> +		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,
> +				      port_priv->reg_width,
> +				      USB_CTRL_SET_TIMEOUT);
> +	}
> +
> +	if (ret == port_priv->reg_width) {
> +		memcpy(val, dmabuf, port_priv->reg_width);

But here you copy ->reg_width bytes in?  How do you know val can hold
that much?  It's only set to be 1, so you copy 1 byte to a 16bit value?
What part of the 16bits did you just copy those 8 bits to (hint, think
cpu endian issues...)

That feels really really odd and a bit broken.

> --- /dev/null
> +++ b/drivers/usb/serial/xr_serial.h
> @@ -0,0 +1,103 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */

Are you sure about the "+"?  I have to ask :)

> +
> +#ifndef __LINUX_USB_SERIAL_XR_SERIAL_H
> +#define __LINUX_USB_SERIAL_XR_SERIAL_H

As you will drop this file, just a general statement, no need for
__LINUX as this is all Linux :)

thanks,

greg k-h