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.c...@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.c...@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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