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

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 16 Feb 2010 10:51:23 +0100
Rodolfo Giometti <giometti@linux.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.