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93e9ad9850
Ever since commit 3a06c7ac24 ("posix-clocks: Remove interval timer
facility and mmap/fasync callbacks") the possibility of PHC based
posix timers has been removed. In addition it will probably never
make sense to implement this functionality.
This patch removes the misleading text which seems to suggest that
posix timers for PHC devices will ever be a thing.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
87 lines
3.5 KiB
Plaintext
87 lines
3.5 KiB
Plaintext
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* PTP hardware clock infrastructure for Linux
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This patch set introduces support for IEEE 1588 PTP clocks in
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Linux. Together with the SO_TIMESTAMPING socket options, this
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presents a standardized method for developing PTP user space
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programs, synchronizing Linux with external clocks, and using the
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ancillary features of PTP hardware clocks.
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A new class driver exports a kernel interface for specific clock
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drivers and a user space interface. The infrastructure supports a
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complete set of PTP hardware clock functionality.
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+ Basic clock operations
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- Set time
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- Get time
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- Shift the clock by a given offset atomically
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- Adjust clock frequency
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+ Ancillary clock features
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- Time stamp external events
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- Period output signals configurable from user space
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- Synchronization of the Linux system time via the PPS subsystem
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** PTP hardware clock kernel API
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A PTP clock driver registers itself with the class driver. The
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class driver handles all of the dealings with user space. The
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author of a clock driver need only implement the details of
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programming the clock hardware. The clock driver notifies the class
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driver of asynchronous events (alarms and external time stamps) via
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a simple message passing interface.
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The class driver supports multiple PTP clock drivers. In normal use
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cases, only one PTP clock is needed. However, for testing and
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development, it can be useful to have more than one clock in a
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single system, in order to allow performance comparisons.
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** PTP hardware clock user space API
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The class driver also creates a character device for each
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registered clock. User space can use an open file descriptor from
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the character device as a POSIX clock id and may call
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clock_gettime, clock_settime, and clock_adjtime. These calls
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implement the basic clock operations.
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User space programs may control the clock using standardized
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ioctls. A program may query, enable, configure, and disable the
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ancillary clock features. User space can receive time stamped
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events via blocking read() and poll().
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** Writing clock drivers
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Clock drivers include include/linux/ptp_clock_kernel.h and register
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themselves by presenting a 'struct ptp_clock_info' to the
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registration method. Clock drivers must implement all of the
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functions in the interface. If a clock does not offer a particular
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ancillary feature, then the driver should just return -EOPNOTSUPP
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from those functions.
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Drivers must ensure that all of the methods in interface are
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reentrant. Since most hardware implementations treat the time value
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as a 64 bit integer accessed as two 32 bit registers, drivers
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should use spin_lock_irqsave/spin_unlock_irqrestore to protect
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against concurrent access. This locking cannot be accomplished in
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class driver, since the lock may also be needed by the clock
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driver's interrupt service routine.
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** Supported hardware
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+ Freescale eTSEC gianfar
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- 2 Time stamp external triggers, programmable polarity (opt. interrupt)
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- 2 Alarm registers (optional interrupt)
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- 3 Periodic signals (optional interrupt)
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+ National DP83640
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- 6 GPIOs programmable as inputs or outputs
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- 6 GPIOs with dedicated functions (LED/JTAG/clock) can also be
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used as general inputs or outputs
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- GPIO inputs can time stamp external triggers
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- GPIO outputs can produce periodic signals
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- 1 interrupt pin
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+ Intel IXP465
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- Auxiliary Slave/Master Mode Snapshot (optional interrupt)
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- Target Time (optional interrupt)
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