• Vladimir Oltean's avatar
    net: dsa: sja1105: Add support for the PTP clock · bb77f36a
    Vladimir Oltean authored
    The design of this PHC driver is influenced by the switch's behavior
    w.r.t. timestamping.  It exposes two PTP counters, one free-running
    (PTPTSCLK) and the other offset- and frequency-corrected in hardware
    through PTPCLKVAL, PTPCLKADD and PTPCLKRATE.  The MACs can sample either
    of these for frame timestamps.
    
    However, the user manual warns that taking timestamps based on the
    corrected clock is less than useful, as the switch can deliver corrupted
    timestamps in a variety of circumstances.
    
    Therefore, this PHC uses the free-running PTPTSCLK together with a
    timecounter/cyclecounter structure that translates it into a software
    time domain.  Thus, the settime/adjtime and adjfine callbacks are
    hardware no-ops.
    
    The timestamps (introduced in a further patch) will also be translated
    to the correct time domain before being handed over to the userspace PTP
    stack.
    
    The introduction of a second set of PHC operations that operate on the
    hardware PTPCLKVAL/PTPCLKADD/PTPCLKRATE in the future is somewhat
    unavoidable, as the TTEthernet core uses the corrected PTP time domain.
    However, the free-running counter + timecounter structure combination
    will suffice for now, as the resulting timestamps yield a sub-50 ns
    synchronization offset in steady state using linuxptp.
    
    For this patch, in absence of frame timestamping, the operations of the
    switch PHC were tested by syncing it to the system time as a local slave
    clock with:
    
    phc2sys -s CLOCK_REALTIME -c swp2 -O 0 -m -S 0.01
    Signed-off-by: default avatarVladimir Oltean <olteanv@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    bb77f36a
sja1105.h 6.01 KB