linux-usb.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Patong Yang <patong.mxl@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: pyang@maxlinear.com, johan@kernel.org, linux-usb@vger.kernel.org
Subject: Driver for MaxLinear/Exar USB (UART) Serial Adapters
Date: Thu, 16 Aug 2018 01:28:54 -0700	[thread overview]
Message-ID: <20180816082854.GA25531@linux1804-desktop> (raw)

On Thu, Aug 16, 2018 at 08:34:47AM +0200, Greg KH wrote:
> 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?

The basic TX/RX functionality works fine now with the cdc-acm driver.
That's the driver that is loaded because it's advertised as a cdc-acm
compatible device in the device descriptors.    

However, the cdc-acm driver (and spec) does not have support all of the 
features in the MaxLinear/Exar USB UARTs.  Hence the reason for a separate
and new driver.  

Features not supported by the cdc-acm driver are 
enabling/disabling flow control, enabling/disabling RS-485 mode, 
GPIOs and GPIO modes, etc. Support for these features had to be added in this
new driver.  

Please let me know if there are any futher questions and advise on how
to proceed.

Thanks,
Patong

             reply	other threads:[~2018-08-16  8:28 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-16  8:28 Patong Yang [this message]
  -- strict thread matches above, loose matches on Subject: below --
2018-08-16 10:05 Driver for MaxLinear/Exar USB (UART) Serial Adapters Greg Kroah-Hartman
2018-08-16  8:26 Oliver Neukum
2018-08-16  6:34 Greg Kroah-Hartman
2018-08-16  5:56 Patong Yang
2018-07-26 10:57 Greg Kroah-Hartman
2018-07-25  7:38 Oliver Neukum
2018-07-24 22:36 Patong Yang
2018-04-06 14:45 Driver for MaxLinear/Exar USB (UART) Serial adapters Greg Kroah-Hartman
2018-04-05  7:38 Oliver Neukum
2018-04-05  6:26 Greg Kroah-Hartman
2018-04-04  8:00 Greg Kroah-Hartman
2018-04-04  7:59 Greg Kroah-Hartman
2018-04-04  7:38 Oliver Neukum
2018-04-04  7:06 Patong Yang

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180816082854.GA25531@linux1804-desktop \
    --to=patong.mxl@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=johan@kernel.org \
    --cc=linux-usb@vger.kernel.org \
    --cc=pyang@maxlinear.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).