ppc: clocksource doc vs. implementation?

Martin Lund mgl at doredevelopment.dk
Thu Nov 5 09:15:07 EST 2009


Working on porting to mpc83xx I've found that the ppc related part of 
the porting.txt documentation seems to contradict the implementation for 
time keeping.

Snip from Documentation/porting.txt:

- Add a clocksource for your system. PowerPCs have a generic decrementer
  counter, so if you have a PowerPC aou have nothing to do here. on ARM
  this is SoC dependend. See Documentation/timekeeping.txt for further

Snip from ppc/mach-mpc5xxx/start.S:

    /* I guess we could implement decrementer, and may have
     * to someday for timekeeping.

I couldn't find trace of any u-boot-v2 ppc code using the time base 
decrementer or incrementer registers anywhere so I assume the time 
keeping support for the current ppc is missing?

I assume that the correct course of action is to implement the 
clocksource_read() function which reads out time counter using the 
incrementing time base register?


Martin Lund, Senior Software Consultant
DoréDevelopment ApS, Ved Stranden 1, 9560 Hadsund, DK-Denmark
Phone: +45 51 92 84 24, Email: mgl at doredevelopment.dk
WWW: http://www.doredevelopment.dk

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