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Date: Mon, 19 Feb 2007 18:56:20 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: Rodolfo Giometti <giometti@...eenne.com> CC: linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/1] LinuxPPS: Pulse per Second support for Linux Rodolfo Giometti wrote: > > Please read the following consideratios before sending to /dev/null! > :) > > RFC considerations > ------------------ > > While implementing a PPS API as RFC 2783 defines and using an embedded > CPU GPIO-Pin as physical link to the signal, I encountered a deeper > problem: > > At startup it needs a file descriptor as argument for the function > time_pps_create(). > > This implies that the source has a /dev/... entry. This assumption is > ok for the serial and parallel port, where you can do something > usefull beside(!) the gathering of timestamps as it is the central > task for a PPS-API. But this assumption does not work for a single > purpose GPIO line. In this case even basic file-related functionality > (like read() and write()) makes no sense at all and should not be a > precondition for the use of a PPS-API. > It's not a precondition for a file descriptor, either. There are plenty of ioctl-only device drivers in existence. Furthermore, a file descriptor doesn't imply a device entry. Consider pipe(2), for example. As far as the kernel is concerned, a file handle is a nice, uniform system for providing communication between the kernel and user space. It doesn't matter if one can read() or write() on it; it's perfectly normal to support only a subset of the normal operations. -hpa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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