linux-kernel - Re: [PATCH 6/8] pps: serial clients support.

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Message-Id: <20100219135359.a5c195ea.akpm@linux-foundation.org>
Date:	Fri, 19 Feb 2010 13:53:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rodolfo Giometti <giometti@...ux.it>
Cc:	linux-kernel@...r.kernel.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>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Alexander Gordeev <lasaine@....cs.msu.su>
Subject: Re: [PATCH 6/8] pps: serial clients support.

On Tue, 16 Feb 2010 10:51:23 +0100
Rodolfo Giometti <giometti@...ux.it> wrote:

> Adds support, by using the PPS line discipline, for the PPS sources
> connected with the CD (Carrier Detect) pin of a serial port.
> 
> ...
>
> +static int (*n_tty_open)(struct tty_struct *tty);
> +
> +static int pps_tty_open(struct tty_struct *tty)
> +{
> +	struct pps_source_info info;
> +	struct tty_driver *drv = tty->driver;
> +	int index = tty->index + drv->name_base;
> +	int ret;
> +
> +	info.owner = THIS_MODULE;
> +	info.dev = NULL;
> +	snprintf(info.name, PPS_MAX_NAME_LEN, "%s%d", drv->driver_name, index);
> +	snprintf(info.path, PPS_MAX_NAME_LEN, "/dev/%s%d", drv->name, index);
> +	info.mode = PPS_CAPTUREBOTH | \
> +			PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
> +			PPS_CANWAIT | PPS_TSFMT_TSPEC;
> +
> +	ret = pps_register_source(&info, PPS_CAPTUREBOTH | \
> +				PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
> +	if (ret < 0) {
> +		pr_err("cannot register PPS source \"%s\"\n", info.path);
> +		return ret;
> +	}
> +	tty->disc_data = (void *) ret;
> +
> +	/* Should open N_TTY ldisc too */
> +	ret = n_tty_open(tty);
> +	if (ret < 0)
> +		pps_unregister_source((int) tty->disc_data);
> +
> +	pr_info("PPS source #%d \"%s\" added\n", ret, info.path);
> +
> +	return 0;
> +}

hm.  The n_tty_open/close layering is a bit grubby but I guess we don't
have a need to create anything more comprehensive at this stage.

A small stylistic thing: the code's a bit confusing at present because
the names n_tty_open/n_tty_close are identical to the global functions
over in n_tty.c.  A user of ctags will be tricked.  Also, the _way_ in
which these function pointers are called:

	ret = n_tty_open(tty);

make it look like the code is calling
drivers/char/n_tty.c:n_tty_open().  Except it isn't.

So I think it's better to do it with

	ret = (*n_tty_open)(tty);

to avoid misleading the reader.

And perhaps to rename these variables to avoid the duplication with the
global functions.


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