[PATCH] 8250_pci: Prevent Exar/RTD Boards from binding.

From: Rob Groner <hidden>
Date: 2015-11-11 18:15:38

-----Original Message-----
From: Greg KH [mailto:greg at kroah.com]
Sent: Wednesday, November 11, 2015 12:32 PM
To: Rob Groner <redacted>
Cc: kernelnewbies at kernelnewbies.org
Subject: Re: [PATCH] 8250_pci: Prevent Exar/RTD Boards from binding.

On Wed, Nov 11, 2015 at 03:46:23PM +0000, Rob Groner wrote:

quoted

-----Original Message-----
From: kernelnewbies-bounces at kernelnewbies.org

[mailto:kernelnewbies-

quoted

bounces at kernelnewbies.org] On Behalf Of Rob Groner
Sent: Monday, October 26, 2015 8:28 AM
To: Greg KH <redacted>
Cc: kernelnewbies at kernelnewbies.org
Subject: RE: [PATCH] 8250_pci: Prevent Exar/RTD Boards from binding.

quoted

-----Original Message-----
From: Greg KH [mailto:greg at kroah.com]
Sent: Monday, September 28, 2015 10:12 AM
To: Rob Groner <redacted>
Cc: Valdis.Kletnieks at vt.edu; kernelnewbies at kernelnewbies.org
Subject: Re: [PATCH] 8250_pci: Prevent Exar/RTD Boards from binding.

On Mon, Sep 28, 2015 at 08:53:49AM -0400, Rob Groner wrote:

quoted

On Fri, 2015-09-25 at 17:45 -0700, Greg KH wrote:

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On Fri, Sep 25, 2015 at 03:21:46PM -0400, Rob Groner wrote:

quoted

On 09/25/2015 03:14 PM, Greg KH wrote:

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On Fri, Sep 25, 2015 at 07:08:32PM +0000, Rob Groner wrote:

quoted

-----Original Message-----
From: Greg KH [mailto:greg at kroah.com]
Sent: Friday, September 25, 2015 2:37 PM
To: Rob Groner <redacted>
Cc: Valdis.Kletnieks at vt.edu;
kernelnewbies at kernelnewbies.org
Subject: Re: [PATCH] 8250_pci: Prevent Exar/RTD Boards
from

binding.

quoted

On Fri, Sep 25, 2015 at 05:37:03PM +0000, Rob Groner wrote:

quoted

-----Original Message-----
From: Valdis.Kletnieks at vt.edu
[mailto:Valdis.Kletnieks at vt.edu]
Sent: Friday, September 25, 2015 12:48 PM
To: Rob Groner <redacted>
Cc: kernelnewbies at kernelnewbies.org
Subject: Re: [PATCH] 8250_pci: Prevent Exar/RTD Boards
from

binding.

quoted

On Fri, 25 Sep 2015 11:46:29 -0400, Rob Groner said:

quoted

Serial boards made by RTD using the Exar XR17V358
chip rely on the extra capabilities of the
Exar-provided driver to allow configuration of the
board.  When support for the Exar chip was added to
the kernel 8250_pci driver, this then prevented easy
use of the board by customers for anything other than
standard serial usage

in RS232 mode.

quoted

Was it your intent to also prevent the use of this
board in standard serial usage in RS232 mode (which
I'd expect is the most common use

case)?

quoted

That is a byproduct of giving the non-average user the
ability to reconfigure their board.  This will
basically move us back to pre-3.8, where the customer
would simply have to insmod the provided Exar driver.
The small inconvenience to that more common user seems
(to us in Tech
Support) outweighed by the much greater inconvenience
to the user who

wants to reconfigure.

quoted

Where is the exar driver, in the kernel already?

confused,

I'm sorry for the confusion.  Let me summup:

We produce a serial port board that uses the Exar XR17V358

chip.

quoted

The board features a jumperless configuration so that to change
the board from RS232 to RS422/RS485, you use the GPIO available on
the Exar chip, via the Exar driver.  That driver is provided by
Exar (from their website, and repackaged on our website and with the

board).

quoted

Recently, we began to hear from customers who purchased
the

board but could not get the driver to find the board (and thus
could not reconfigure it, nor use the non-standard high baud rates
the chip is capable of).  We discovered that in 3.8, support for
the Exar chip was added to the 8250_pci driver, thus binding it to the

kernel.

quoted

Until (and probably if) Exar decides to submit their
driver to the

kernel, then it leaves us with a problem that we didn't have prior
to 3.8...namely that the board won't do what it is advertised to
do unless the customer rebuilds the kernel (that is the only
supported workaround from Exar).  The only other workaround we
know of (unbind) has met with mixed success which I won't go into
unless you want me to, and is already resisted by some customers.

quoted

The goal of this patch is to get to a point where a
customer can install

Linux and have full use of this RTD board (using the driver
Exar/RTD provides).  No one who has an RTD board is going to feel
this is an inconvenience.

quoted

Can you point me at the driver and I'll be glad to add it
to the kernel so that the proper driver will bind to the
device and this will not be an issue for users?

thanks,

greg k-h

That would be WONDERFUL.

https://na01.safelinks.protection.outlook.com/?url=https%3a%
2f%2

fwww.exar.com%2fcommon%2fcontent%2fdocument.ashx%3fid%3d20121&

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da
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ta=01%7c01%7crgroner%40rtd.com%7c261e5150b71d4b17e91308d2de03148

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e%7c16f82b7977b8423dbafdd6c19032e267%7c0&sdata=Tl%2br4Vjgut%2bRh

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3nam6wTMwbpBDpqIW%2fb2dzsTJtE0A4%3d

At first glance, the driver looks pretty good.  Let me do a
bit of cleanup on it for mostly coding style changes and
removing some old api support and see what the patch is.

Would you mind testing it if I make a patch, given that I
don't have the hardware and you do?  :)

thanks,

greg k-h

I don't mind in the slightest, it's the least I can do!  I've
got my test station ready and have 3 different CPUs I can test
with.  Being new to the whole patching thing, I may need a few
hints and helps to make sure I apply the patch correctly...

Will it be showing up here in kernel newbies mailing list, or
linux-serial, or other?

How about let's take it to linux-serial, and I'll cc: you as well,
that's the proper place for this.

Note, the driver does do some "odd" things in that it has some

"custom"

quoted

ioctls for unknown reasons, and it grabs a major number of another
driver, both things that I can't accept upstream.  It also seems
to duplicate a lot of existing code, so maybe it doesn't really
need to be a separate driver.  I'll dig around in it and see what
I can come up with,

give me a week or so...

quoted

thanks,

greg k-h

I know you're incredibly busy, so I added as much "so" to the week as I

could.

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Any way I can help with this endeavor, other than testing?

Would it be possible to consider my original patch, if putting in the Exar

driver is too time consuming?

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I'd rather have the Exar driver than my patch, but I'd also rather have my

patch than the current situation.

I don't remember what your "original patch" was, sorry.

greg k-h

My patch prevented RTD-subvendor boards that have the Exar serial chip on them from being bound to the kernel 8250_pci driver.  That allows our customers to insert the Exar-provided driver which then gives them access to configuring the board.

You asked for a link to the Exar driver, and you graciously offered to put the driver into the kernel, which would also solve our problem.

Thank you,

Rob G.

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