linux-kernel - Re: [PATCH 05/10] ldisc: new dcd_change() method for line disciplines.

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Date:	Wed, 20 Aug 2008 01:05:23 +0200
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Dave Jones <davej@...hat.com>, Sam Ravnborg <sam@...nborg.org>,
	Greg KH <greg@...ah.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH 05/10] ldisc: new dcd_change() method for line
	disciplines.

On Tue, Aug 19, 2008 at 11:38:57PM +0100, Alan Cox wrote:
> On Wed, 20 Aug 2008 00:49:31 +0200
> Rodolfo Giometti <giometti@...eenne.com> wrote:
> 
> > On Tue, Aug 19, 2008 at 10:53:22PM +0100, Alan Cox wrote:
> > > > + * void (*dcd_change)(struct uart_port *port, unsigned int status,
> > > > + * 			struct timespec *ts)
> > > > + *
> > > > + *	Tells the discipline that the DCD pin has changed its status and
> > > > + *	the relative timestamp. Pointer ts can be NULL.
> > > >   */
> > > 
> > > uart_port is a specific property of a few random types of interface, pass
> > > a tty struct up. Otherwise looks fine. Might one day expand it to a more
> > > generic change type and pass info on what changed but thats a future
> > > mystery.
> > 
> > How can I get the struct uart_port pointer starting from struct
> > tty_struct one?
> 
> A tty may not even have a uart structure. Why do you need to know the
> interrupt (if such a concept even exists for the given tty) ?

If you look at patch 9
(0009-PPS-low-level-IRQ-timestamps-recording.patch) you can see that
we add a (dirty?) trick to improve PPS precision a lot: we record all
IRQ timestamps into static array and then we return those values
instead of ones passed by dcd_change()...

Maybe I can solve the problem defining dcd_change() as follow:

   void (*dcd_change)(struct tty_struct *tty, unsigned int status,
                        void *data)

and then passing the timestamp or struct uart_port pointer?

Thanks,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
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