Re: set_rtc_time() cleanup / normalization

On Tue, May 13, 2003 at 09:52:22AM +0200, Geert Uytterhoeven wrote:

On Mon, 12 May 2003, Wolfgang Denk wrote:

quoted

I would like to find out if there is some consensus about the use  of
set_rtc_time() in the timer interrupt handler.

    Note: this question relates to a thread that was started by
    Stephen Johnson on Tue, 22 Apr 2003; see message:
    http://lists.linuxppc.org/linuxppc-embedded/200304/msg00233.html

The problem: some systems use RTC chips which  are  attached  to  the
system  using an I2C bus (or similar). To control the device you will
have to setup one or more I2C transactions, which usually  result  in
one or more interrupts which must be processed.

Depending on which architecture and/or board you are using, there may
or may not be a call to set_rtc_time()  be  performed  in  the  timer
interrupt  handler.  This  call  will  happen  every  11 minutes (659
seconds, to be precise) - see "arch/ppc/kernel/time.c".


I would like to know if there is a rationale  in  putting  this  call
into a general part of the source code.

Other architectures handle this differently. For example, in the  ARM
kernel   tree  the  timer  interrupt  implementation  is  essentially
board-specific (located in a include/asm/arch-.../time.h file).  Some
ARM  boards'  timer interrupt handlers do call set_rtc_time(), others
don't.

Shouldn't we do the same on PPC?

Or maybe we should delete this code completely? If somebody wants  to
sync the RTC against the system time a simple daemon or cron job (for
example calling "hwclock --systohc" every 11 minutes) would result in
more or less identical results.

On m68k, we removed that part because it confused NTP. Richard Zidlicky can
probably tell more about that.

I certainly would like to know the details of this. I believe it may
be fixing the symptom rather than the cause (an NTP bug).

	Gabriel

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