Driver for MaxLinear/Exar USB (UART) Serial Adapters

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Aug 15, 2018 at 10:56:47PM -0700, Patong Yang wrote:
> Greg,
> 
> Please see my response inline below.
> 
> Patong
> 
> > But there is a bigger problem here:
> > 
> > > +	xrusb_tty_driver = alloc_tty_driver(XRUSB_TTY_MINORS);
> > > +	if (!xrusb_tty_driver)
> > > +		return -ENOMEM;
> > 
> > Why are you not using the usb serial core here?  You need to do that,
> > not try to provide your own custom tty driver.  That way userspace
> > programs will "just work" with your new device, no changes needed as
> > your major/minor number and device name would be custom only for your
> > device, which is not acceptable.
> 
> The MaxLinear/USB serial devices support the CDC-ACM commands.
> Therefore, we used the cdc-acm driver instead of the usb serial driver
> as the starting point for developing the driver.  We replaced "ACM" 
> with "XRUSB" throughout the driver.  Would it be better if we just used 
> the same major/minor number as the CDC-ACM driver since it was based on
> the cdc-acm driver?  

No, just use the cdc-acm driver itself and add your product/device id to
it and it should work just fine.  Why do you need to write a whole new
driver at all?

thanks,

greg k-h