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    SubjectRe: [PATCH] arm64: kernel: compiling issue, need 'EXPORT_SYMBOL_GPL(read_current_timer)'
    On 05/20/2013 05:56 PM, Will Deacon wrote:
    > On Mon, May 20, 2013 at 08:15:04AM +0100, Marc Zyngier wrote:
    >> On Mon, 20 May 2013 14:48:05 +0800, Chen Gang <gang.chen@asianux.com>
    >> wrote:
    >>> Need 'EXPORT_SYMBOL_GPL(read_current_timer)' if build with allmodconfig.
    >>>
    >>> The related error:
    >>> ERROR: "read_current_timer" [lib/rbtree_test.ko] undefined!
    >>> ERROR: "read_current_timer" [lib/interval_tree_test.ko] undefined!
    >>> ERROR: "read_current_timer" [fs/ext4/ext4.ko] undefined!
    >>> ERROR: "read_current_timer" [crypto/tcrypt.ko] undefined!
    >>>
    >>>
    >>> Signed-off-by: Chen Gang <gang.chen@asianux.com>
    >>> ---
    >>> arch/arm64/kernel/time.c | 1 +
    >>> 1 files changed, 1 insertions(+), 0 deletions(-)
    >>>
    >>> diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
    >>> index a551f88..7fcba80 100644
    >>> --- a/arch/arm64/kernel/time.c
    >>> +++ b/arch/arm64/kernel/time.c
    >>> @@ -73,6 +73,7 @@ int read_current_timer(unsigned long *timer_value)
    >>> *timer_value = arch_timer_read_counter();
    >>> return 0;
    >>> }
    >>> +EXPORT_SYMBOL_GPL(read_current_timer);
    >>>
    >>> void __init time_init(void)
    >>> {
    >>
    >> While this solves the problem, I'm not sure this is the best fix. The real
    >> issue is with get_cycles, which is a macro around read_current_timer.
    >>
    >> AArch32 exports it because of the number of timer implementations. On
    >> arm64, we should be able to just return CNTVCT_EL0.
    >>
    >> Catalin, Will, what do you think?
    >
    > Should be ok once the arch timer driver has moved exclusively to virtual
    > time. I'm also not sure we even need to implement read_current_timer() --
    > it's only used for delay-loop calibration, which we don't need for the
    > arch timer.
    >

    For whether we need implement read_current_timer():

    many platforms have implemented it (openrisc, arm, sparc, hexagon, avr32, x86).
    it is called by init/calibrate.c when 'ARCH_HAS_READ_CURRENT_TIMER' is defined.
    since arm64 can implement it, better to provide it as an architect features to let outside use.

    For the implementation of read_current_timer():

    it has to face various configurations
    (e.g. CONFIG_ARM_ARCH_TIMER, arch_timer_read_zero, arch_counter_get_cntvct, arch_counter_get_cntpct)
    so better still use variable instead of.
    (excuse me, I do not know what is 'CNTVCT_EL0', is it like a constant number ?)

    For the implementation of get_cycles()

    if read_current_timer() is provided,
    better to let get_cycles() to call it, instead of implement once again.



    Thanks.
    --
    Chen Gang

    Asianux Corporation


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