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

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Message-Id: <20100804163430.a87027c6.akpm@linux-foundation.org>
Date:	Wed, 4 Aug 2010 16:34:30 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alexander Gordeev <lasaine@....cs.msu.su>
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

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.

>
> ...
>
> +{
> +	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.

>
> ...
>
--
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