On Wed, Apr 29, 2020 at 11:29:04AM +0200, Greg KH wrote: > On Wed, Apr 29, 2020 at 01:10:26PM +0530, Manivannan Sadhasivam wrote: > > Hi Greg, > > > > On Wed, Apr 29, 2020 at 09:20:36AM +0200, Greg KH wrote: > > > On Wed, Apr 29, 2020 at 01:26:50AM +0530, mani@xxxxxxxxxx wrote: > > > > From: Manivannan Sadhasivam <mani@xxxxxxxxxx> > > > > > > > > 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@xxxxxxxxx> > > > > + * > > > > + * Copyright (c) 2020 Manivannan Sadhasivam <mani@xxxxxxxxxx> > > > > + */ > > > > + > > > > +#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. > > > > > > > Yeah but since this driver can support multiple series of XR chips (they > > might have separate register definitions and such), I thought it is a good > > idea to have a header file to keep the driver sane. But can club it to the > > source file for now. > > Don't worry about future stuff, focus on what you need to do now :) > Alright, will do :) > > > > +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? > > > > > > > Explanation below... > > > > > > + 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. > > > > > > > Right. The reason is, the other series which can be supported by this driver > > have different register widths. For instance XR2280x. I haven't used them > > personally but seen this in initial driver. So I just used the max u16 type > > to make the reg_{set/get} routines work with those. > > Drop the whole "different register width" stuff for now, as the driver > does not support it and it adds additional complexity that is hard to > review for no good reason. If you want to add support for new devices > later, _then_ we can add support for that. > > Don't over-engineer :) > Sure! > > But agree, I should've used le16_to_cpu() cast to avoid endian issues. > > You have to, the code is broken as-is right now. > We don't need the conversion if u8 is used everywhere :) Thanks, Mani > > If you think this hack is not required now, I can just use u8 and worry about > > compatibility later. > > Please do so. > > thanks, > > greg k-h
