linux-kernel - Re: [PATCHv3 15/16] pps: add parallel port PPS client

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Message-ID: <20100805164829.33855c7a@desktopvm.lvknet>
Date:	Thu, 5 Aug 2010 16:48:29 +0400
From:	Alexander Gordeev <lasaine@....cs.msu.su>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	"Nikita V\. Youshchenko" <yoush@...msu.su>,
	linuxpps@...enneenne.com, Rodolfo Giometti <giometti@...eenne.com>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCHv3 15/16] pps: add parallel port PPS client

В Wed, 4 Aug 2010 16:34:30 -0700
Andrew Morton <akpm@...ux-foundation.org> пишет:

> On Thu,  5 Aug 2010 01:06:52 +0400
> Alexander Gordeev <lasaine@....cs.msu.su> wrote:
> 
> > Add parallel port PPS client. It uses a standard method for capturing
> > timestamps for assert edge transitions: getting a timestamp soon after
> > an interrupt has happened. This is not a very precise source of time
> > information due to interrupt handling delays. However, timestamps for
> > clear edge transitions are much more precise because the interrupt
> > handler continuously polls hardware port until the transition is done.
> > Hardware port operations require only about 1us so the maximum error
> > should not exceed this value. This was my primary goal when developing
> > this client.
> > Clear edge capture could be disabled using clear_wait parameter.
> > 
> >
> > ...
> >
> > +
> > +#define SIGNAL_IS_SET(port) \
> > +	((port->ops->read_status(port) & PARPORT_STATUS_ACK) != 0)
> 
> This could (and hence should) be implemented in a regular old C
> function.

Ok, thanks!

> >
> > ...
> >
> > +{
> > +	struct pps_client_pp *device;
> > +	struct pps_source_info info = {
> > +		.name		= DRVNAME,
> > +		.path		= "",
> > +		.mode		= PPS_CAPTUREBOTH | \
> > +				  PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
> > +				  PPS_ECHOASSERT | PPS_ECHOCLEAR | \
> > +				  PPS_CANWAIT | PPS_TSFMT_TSPEC,
> > +		.echo		= pps_echo,
> > +		.owner		= THIS_MODULE,
> > +		.dev		= NULL
> > +	};
> > +
> > +	device = kzalloc(sizeof(struct pps_client_pp), GFP_KERNEL);
> > +	if (!device) {
> > +		pr_err(DRVNAME ": memory allocation failed, not attaching\n");
> > +		return;
> 
> eww.  parport_driver.attach() returns void so there's no way to
> propagate the error code back.  That sucks a bit.

IMHO, the whole parport thing currently sucks quite a bit.

-- 
  Alexander

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