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ptp: Added a brand new class driver for ptp clocks.

This patch adds an infrastructure for hardware clocks that implement
IEEE 1588, the Precision Time Protocol (PTP). A class driver offers a
registration method to particular hardware clock drivers. Each clock is
presented as a standard POSIX clock.

The ancillary clock features are exposed in two different ways, via
the sysfs and by a character device.

Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: John Stultz <john.stultz@linaro.org>
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1 parent caebc16 commit d94ba80ebbea17f036cecb104398fbcd788aa742 @richardcochran richardcochran committed with johnstultz-work Apr 22, 2011
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+What: /sys/class/ptp/
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This directory contains files and directories
+ providing a standardized interface to the ancillary
+ features of PTP hardware clocks.
+
+What: /sys/class/ptp/ptpN/
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This directory contains the attributes of the Nth PTP
+ hardware clock registered into the PTP class driver
+ subsystem.
+
+What: /sys/class/ptp/ptpN/clock_name
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file contains the name of the PTP hardware clock
+ as a human readable string.
+
+What: /sys/class/ptp/ptpN/max_adjustment
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file contains the PTP hardware clock's maximum
+ frequency adjustment value (a positive integer) in
+ parts per billion.
+
+What: /sys/class/ptp/ptpN/n_alarms
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file contains the number of periodic or one shot
+ alarms offer by the PTP hardware clock.
+
+What: /sys/class/ptp/ptpN/n_external_timestamps
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file contains the number of external timestamp
+ channels offered by the PTP hardware clock.
+
+What: /sys/class/ptp/ptpN/n_periodic_outputs
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file contains the number of programmable periodic
+ output channels offered by the PTP hardware clock.
+
+What: /sys/class/ptp/ptpN/pps_avaiable
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file indicates whether the PTP hardware clock
+ supports a Pulse Per Second to the host CPU. Reading
+ "1" means that the PPS is supported, while "0" means
+ not supported.
+
+What: /sys/class/ptp/ptpN/extts_enable
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This write-only file enables or disables external
+ timestamps. To enable external timestamps, write the
+ channel index followed by a "1" into the file.
+ To disable external timestamps, write the channel
+ index followed by a "0" into the file.
+
+What: /sys/class/ptp/ptpN/fifo
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This file provides timestamps on external events, in
+ the form of three integers: channel index, seconds,
+ and nanoseconds.
+
+What: /sys/class/ptp/ptpN/period
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This write-only file enables or disables periodic
+ outputs. To enable a periodic output, write five
+ integers into the file: channel index, start time
+ seconds, start time nanoseconds, period seconds, and
+ period nanoseconds. To disable a periodic output, set
+ all the seconds and nanoseconds values to zero.
+
+What: /sys/class/ptp/ptpN/pps_enable
+Date: September 2010
+Contact: Richard Cochran <richardcochran@gmail.com>
+Description:
+ This write-only file enables or disables delivery of
+ PPS events to the Linux PPS subsystem. To enable PPS
+ events, write a "1" into the file. To disable events,
+ write a "0" into the file.
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+
+* PTP hardware clock infrastructure for Linux
+
+ This patch set introduces support for IEEE 1588 PTP clocks in
+ Linux. Together with the SO_TIMESTAMPING socket options, this
+ presents a standardized method for developing PTP user space
+ programs, synchronizing Linux with external clocks, and using the
+ ancillary features of PTP hardware clocks.
+
+ A new class driver exports a kernel interface for specific clock
+ drivers and a user space interface. The infrastructure supports a
+ complete set of PTP hardware clock functionality.
+
+ + Basic clock operations
+ - Set time
+ - Get time
+ - Shift the clock by a given offset atomically
+ - Adjust clock frequency
+
+ + Ancillary clock features
+ - One short or periodic alarms, with signal delivery to user program
+ - Time stamp external events
+ - Period output signals configurable from user space
+ - Synchronization of the Linux system time via the PPS subsystem
+
+** PTP hardware clock kernel API
+
+ A PTP clock driver registers itself with the class driver. The
+ class driver handles all of the dealings with user space. The
+ author of a clock driver need only implement the details of
+ programming the clock hardware. The clock driver notifies the class
+ driver of asynchronous events (alarms and external time stamps) via
+ a simple message passing interface.
+
+ The class driver supports multiple PTP clock drivers. In normal use
+ cases, only one PTP clock is needed. However, for testing and
+ development, it can be useful to have more than one clock in a
+ single system, in order to allow performance comparisons.
+
+** PTP hardware clock user space API
+
+ The class driver also creates a character device for each
+ registered clock. User space can use an open file descriptor from
+ the character device as a POSIX clock id and may call
+ clock_gettime, clock_settime, and clock_adjtime. These calls
+ implement the basic clock operations.
+
+ User space programs may control the clock using standardized
+ ioctls. A program may query, enable, configure, and disable the
+ ancillary clock features. User space can receive time stamped
+ events via blocking read() and poll(). One shot and periodic
+ signals may be configured via the POSIX timer_settime() system
+ call.
+
+** Writing clock drivers
+
+ Clock drivers include include/linux/ptp_clock_kernel.h and register
+ themselves by presenting a 'struct ptp_clock_info' to the
+ registration method. Clock drivers must implement all of the
+ functions in the interface. If a clock does not offer a particular
+ ancillary feature, then the driver should just return -EOPNOTSUPP
+ from those functions.
+
+ Drivers must ensure that all of the methods in interface are
+ reentrant. Since most hardware implementations treat the time value
+ as a 64 bit integer accessed as two 32 bit registers, drivers
+ should use spin_lock_irqsave/spin_unlock_irqrestore to protect
+ against concurrent access. This locking cannot be accomplished in
+ class driver, since the lock may also be needed by the clock
+ driver's interrupt service routine.
+
+** Supported hardware
+
+ + Freescale eTSEC gianfar
+ - 2 Time stamp external triggers, programmable polarity (opt. interrupt)
+ - 2 Alarm registers (optional interrupt)
+ - 3 Periodic signals (optional interrupt)
+
+ + National DP83640
+ - 6 GPIOs programmable as inputs or outputs
+ - 6 GPIOs with dedicated functions (LED/JTAG/clock) can also be
+ used as general inputs or outputs
+ - GPIO inputs can time stamp external triggers
+ - GPIO outputs can produce periodic signals
+ - 1 interrupt pin
+
+ + Intel IXP465
+ - Auxiliary Slave/Master Mode Snapshot (optional interrupt)
+ - Target Time (optional interrupt)
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