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

Wed Nov 11 13:15:38 EST 2015

> -----Original Message-----
> From: Greg KH [mailto:greg at kroah.com]
> Sent: Wednesday, November 11, 2015 12:32 PM
> To: Rob Groner <rgroner at RTD.com>
> 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:
> >
> > > -----Original Message-----
> > > From: kernelnewbies-bounces at kernelnewbies.org
> [mailto:kernelnewbies-
> > > bounces at kernelnewbies.org] On Behalf Of Rob Groner
> > > Sent: Monday, October 26, 2015 8:28 AM
> > > To: Greg KH <greg at kroah.com>
> > > Cc: kernelnewbies at kernelnewbies.org
> > > Subject: RE: [PATCH] 8250_pci: Prevent Exar/RTD Boards from binding.
> > >
> > > > -----Original Message-----
> > > > From: Greg KH [mailto:greg at kroah.com]
> > > > Sent: Monday, September 28, 2015 10:12 AM
> > > > To: Rob Groner <rgroner at RTD.com>
> > > > 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:
> > > > > On Fri, 2015-09-25 at 17:45 -0700, Greg KH wrote:
> > > > > > On Fri, Sep 25, 2015 at 03:21:46PM -0400, Rob Groner wrote:
> > > > > > >
> > > > > > > On 09/25/2015 03:14 PM, Greg KH wrote:
> > > > > > > > On Fri, Sep 25, 2015 at 07:08:32PM +0000, Rob Groner wrote:
> > > > > > > >>> -----Original Message-----
> > > > > > > >>> From: Greg KH [mailto:greg at kroah.com]
> > > > > > > >>> Sent: Friday, September 25, 2015 2:37 PM
> > > > > > > >>> To: Rob Groner <rgroner at RTD.com>
> > > > > > > >>> Cc: Valdis.Kletnieks at vt.edu;
> > > > > > > >>> kernelnewbies at kernelnewbies.org
> > > > > > > >>> Subject: Re: [PATCH] 8250_pci: Prevent Exar/RTD Boards
> > > > > > > >>> from
> > > > binding.
> > > > > > > >>>
> > > > > > > >>> On Fri, Sep 25, 2015 at 05:37:03PM +0000, Rob Groner wrote:
> > > > > > > >>>>> -----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 <rgroner at RTD.com>
> > > > > > > >>>>> Cc: kernelnewbies at kernelnewbies.org
> > > > > > > >>>>> Subject: Re: [PATCH] 8250_pci: Prevent Exar/RTD Boards
> > > > > > > >>>>> from
> > > > binding.
> > > > > > > >>>>>
> > > > > > > >>>>> On Fri, 25 Sep 2015 11:46:29 -0400, Rob Groner said:
> > > > > > > >>>>>> 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.
> > > > > > > >>>>> 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)?
> > > > > > > >>>> 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.
> > > > > > > >>> 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.
> > > > 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).
> > > > > > > >>
> > > > > > > >> 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.
> > > > > > > >>
> > > > > > > >> 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.
> > > > > > > >>
> > > > > > > >> 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.
> > > > > > > > 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&
> > > da
> > > > > > >
> > >
> ta=01%7c01%7crgroner%40rtd.com%7c261e5150b71d4b17e91308d2de03148
> > > > > > >
> > >
> e%7c16f82b7977b8423dbafdd6c19032e267%7c0&sdata=Tl%2br4Vjgut%2bRh
> > > > > > > 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"
> > > > 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...
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > >
> > > I know you're incredibly busy, so I added as much "so" to the week as I
> could.
> > > 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?
> > 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.