LinuxPPS: core support

This patch adds the kernel side of the PPS support currently named
"LinuxPPS".

PPS means "pulse per second" and a PPS source is just a device which
provides a high precision signal each second so that an application can
use it to adjust system clock time.

Common use is the combination of the NTPD as userland program with a GPS
receiver as PPS source to obtain a wallclock-time with sub-millisecond
synchronisation to UTC.

To obtain this goal the userland programs shoud use the PPS API
specification (RFC 2783 - Pulse-Per-Second API for UNIX-like Operating
Systems, Version 1.0) which in part is implemented by this patch.  It
provides a set of chars devices, one per PPS source, which can be used to
get the time signal.  The RFC's functions can be implemented by accessing
to these char devices.

Signed-off-by: Rodolfo Giometti <giometti@linux.it>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg KH <greg@kroah.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 73 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-pps b/Documentation/ABI/testing/sysfs-pps
new file mode 100644
index 000000000000..25028c7bc37d
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-pps
@@ -0,0 +1,73 @@
+What:           /sys/class/pps/
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ directory will contain files and
+                directories that will provide a unified interface to
+                the PPS sources.
+
+What:           /sys/class/pps/ppsX/
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/ directory is related to X-th
+                PPS source into the system. Each directory will
+                contain files to manage and control its PPS source.
+
+What:           /sys/class/pps/ppsX/assert
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/assert file reports the assert events
+                and the assert sequence number of the X-th source in the form:
+
+                        <secs>.<nsec>#<sequence>
+
+                If the source has no assert events the content of this file
+                is empty.
+
+What:           /sys/class/pps/ppsX/clear
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/clear file reports the clear events
+                and the clear sequence number of the X-th source in the form:
+
+                        <secs>.<nsec>#<sequence>
+
+                If the source has no clear events the content of this file
+                is empty.
+
+What:           /sys/class/pps/ppsX/mode
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/mode file reports the functioning
+                mode of the X-th source in hexadecimal encoding.
+
+                Please, refer to linux/include/linux/pps.h for further
+                info.
+
+What:           /sys/class/pps/ppsX/echo
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/echo file reports if the X-th does
+                or does not support an "echo" function.
+
+What:           /sys/class/pps/ppsX/name
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/name file reports the name of the
+                X-th source.
+
+What:           /sys/class/pps/ppsX/path
+Date:           February 2008
+Contact:        Rodolfo Giometti <giometti@linux.it>
+Description:
+                The /sys/class/pps/ppsX/path file reports the path name of
+                the device connected with the X-th source.
+
+                If the source is not connected with any device the content
+                of this file is empty.