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, 122 insertions, 0 deletions

diff --git a/include/linux/pps.h b/include/linux/pps.h
new file mode 100644
index 000000000000..cfe5c7214ec6
--- /dev/null
+++ b/include/linux/pps.h
@@ -0,0 +1,122 @@
+/*
+ * PPS API header
+ *
+ * Copyright (C) 2005-2009   Rodolfo Giometti <giometti@linux.it>
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+#ifndef _PPS_H_
+#define _PPS_H_
+
+#define PPS_VERSION             "5.3.6"
+#define PPS_MAX_SOURCES         16              /* should be enough... */
+
+/* Implementation note: the logical states ``assert'' and ``clear''
+ * are implemented in terms of the chip register, i.e. ``assert''
+ * means the bit is set.  */
+
+/*
+ * 3.2 New data structures
+ */
+
+#define PPS_API_VERS_1          1
+#define PPS_API_VERS            PPS_API_VERS_1  /* we use API version 1 */
+#define PPS_MAX_NAME_LEN        32
+
+/* 32-bit vs. 64-bit compatibility.
+ *
+ * 0n i386, the alignment of a uint64_t is only 4 bytes, while on most other
+ * architectures it's 8 bytes. On i386, there will be no padding between the
+ * two consecutive 'struct pps_ktime' members of struct pps_kinfo and struct
+ * pps_kparams. But on most platforms there will be padding to ensure correct
+ * alignment.
+ *
+ * The simple fix is probably to add an explicit padding.
+ *                                                      [David Woodhouse]
+ */
+struct pps_ktime {
+        __s64 sec;
+        __s32 nsec;
+        __u32 flags;
+};
+#define PPS_TIME_INVALID        (1<<0)  /* used to specify timeout==NULL */
+
+struct pps_kinfo {
+        __u32 assert_sequence;          /* seq. num. of assert event */
+        __u32 clear_sequence;           /* seq. num. of clear event */
+        struct pps_ktime assert_tu;     /* time of assert event */
+        struct pps_ktime clear_tu;      /* time of clear event */
+        int current_mode;               /* current mode bits */
+};
+
+struct pps_kparams {
+        int api_version;                /* API version # */
+        int mode;                       /* mode bits */
+        struct pps_ktime assert_off_tu; /* offset compensation for assert */
+        struct pps_ktime clear_off_tu;  /* offset compensation for clear */
+};
+
+/*
+ * 3.3 Mode bit definitions
+ */
+
+/* Device/implementation parameters */
+#define PPS_CAPTUREASSERT       0x01    /* capture assert events */
+#define PPS_CAPTURECLEAR        0x02    /* capture clear events */
+#define PPS_CAPTUREBOTH         0x03    /* capture assert and clear events */
+
+#define PPS_OFFSETASSERT        0x10    /* apply compensation for assert ev. */
+#define PPS_OFFSETCLEAR         0x20    /* apply compensation for clear ev. */
+
+#define PPS_CANWAIT             0x100   /* can we wait for an event? */
+#define PPS_CANPOLL             0x200   /* bit reserved for future use */
+
+/* Kernel actions */
+#define PPS_ECHOASSERT          0x40    /* feed back assert event to output */
+#define PPS_ECHOCLEAR           0x80    /* feed back clear event to output */
+
+/* Timestamp formats */
+#define PPS_TSFMT_TSPEC         0x1000  /* select timespec format */
+#define PPS_TSFMT_NTPFP         0x2000  /* select NTP format */
+
+/*
+ * 3.4.4 New functions: disciplining the kernel timebase
+ */
+
+/* Kernel consumers */
+#define PPS_KC_HARDPPS          0       /* hardpps() (or equivalent) */
+#define PPS_KC_HARDPPS_PLL      1       /* hardpps() constrained to
+                                           use a phase-locked loop */
+#define PPS_KC_HARDPPS_FLL      2       /* hardpps() constrained to
+                                           use a frequency-locked loop */
+/*
+ * Here begins the implementation-specific part!
+ */
+
+struct pps_fdata {
+        struct pps_kinfo info;
+        struct pps_ktime timeout;
+};
+
+#include <linux/ioctl.h>
+
+#define PPS_GETPARAMS           _IOR('p', 0xa1, struct pps_kparams *)
+#define PPS_SETPARAMS           _IOW('p', 0xa2, struct pps_kparams *)
+#define PPS_GETCAP              _IOR('p', 0xa3, int *)
+#define PPS_FETCH               _IOWR('p', 0xa4, struct pps_fdata *)
+
+#endif /* _PPS_H_ */