From a10203c691eac287664f531b149ddc23056c2f61 Mon Sep 17 00:00:00 2001
From: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Date: Wed, 12 Jan 2011 17:00:58 -0800
Subject: [PATCH] pps: add parallel port PPS client

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.

Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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