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    SubjectRe: [RFC PATCH 0/3] Add accurate boot timing to a Linux system
    Hi,

    Russell King - ARM Linux a écrit :
    > On Fri, Sep 23, 2011 at 04:03:15PM -0700, Simon Glass wrote:
    >> An accurate timer is required to make the numbers meaningful. Many
    >> modern platforms have a microsecond timer. This patch set uses a
    >> function called timer_get_us() to read the timer.
    >
    > Not another 'get a time value' function. Why do we need soo many?
    > We have - at least:
    >
    > ktime_get (and various flavours of it)
    > do_gettimeofday
    > getnstimeofday
    > sched_clock
    >
    > Do we really need yet another one which will have to be multiplexed
    > amongst platforms, requiring scaling and so forth from whatever the
    > platform provides?
    >
    > Remember that ARM timers are virtually all MMIO mapped, which means
    > they don't work during early kernel bringup when the MMU mappings for
    > the hardware have not been setup. (That's the reason stuff like
    > sched_clock for printk doesn't work early.)
    Doesn't cortexA-8 (and A9 ?) have a cycle counter that can be read by
    coprocessor 15 ?

    Couldn't we use that counter for early stuff on those architectures ?


    Matthieu
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