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    SubjectRe: [PATCH 33/36] AArch64: Generic timers support
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    On Thu, Jul 12, 2012 at 12:09 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:

    > On Thu, 12 Jul 2012 02:18:42 +0200, Linus Walleij
    > <linus.ml.walleij@gmail.com> wrote:
    >
    > Hi Linus,
    >
    >> I'm reviewing the only patch I really understand...
    >>
    >> 2012/7/6 Catalin Marinas <catalin.marinas@arm.com>:
    >>
    >>> +/* This isn't really used any more */
    >>> +#define CLOCK_TICK_RATE 1000
    >>
    >> Is it still necessary to even have it there?
    >
    > It is used as part of the LATCH/TICK_* computation in
    > include/linux/jiffies.h. It seems that any value could do, actually, and it
    > only seem to be used in kernel/time/ntp.c. Any guidance on this much
    > appreciated.
    >
    > By the way, there is a very interesting comment about this in
    > arch/ia64/include/asm/timex.h.

    Hmmmm paging John Stultz, TGLX, Deepak Saxena who have been in
    this area...

    >>> + arch_timer_calibrate();
    >>
    >> Why is the ability to get this from a clk not contemplated?
    >> I think this will be common. You could make it optional I think,
    >> just like in the SMP TWD.
    >
    > _calibrate() is a misnomer here. It should really be _get_freq(). But your
    > point still stand, and we could indeed use a clk to obtain the frequency.
    >
    > It should probably be selected in the following order: clock-frequency
    > (DT), clk, CNTFRQ.

    I agree. It can be bolted on later too, just trying to think ahead a bit.

    I'm half-guessing that for mobile embedded with their complex clock trees
    it will likely come from a clk whereas in servers etc there will be one
    big clock for all and it will be fine to use the DT node.

    Yours,
    Linus Walleij


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