Driver for MaxLinear/Exar USB (UART) Serial Adapters

From: Patong Yang <patong.mxl@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: johan@kernel.org, linux-usb@vger.kernel.org, pyang@maxlinear.com
Subject: Driver for MaxLinear/Exar USB (UART) Serial Adapters
Date: Wed, 15 Aug 2018 22:56:47 -0700	[thread overview]
Message-ID: <20180816055647.GA24930@linux1804-desktop> (raw)

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?  

> 
> By doing that, your code will also be much smaller, always a good
> benefit as well.
>