Re: [PATCH] arm64: kernel: compiling issue, need 'EXPORT_SYMBOL_GPL(read_current_timer)'

From: Chen Gang
Date: Tue May 21 2013 - 05:28:14 EST

On 05/21/2013 04:53 PM, Will Deacon wrote:
> On Tue, May 21, 2013 at 05:06:52AM +0100, Chen Gang wrote:
>> On 05/20/2013 05:56 PM, Will Deacon wrote:
>>> 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.
> No, that code is not needed on arm64 because we calibrate the delay loop
> statically using a known timer frequency.
>> 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 ?)
> cntvct_el0 is a system register, which provides the virtual counter value.
>> 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.
> You can implement it as a macro if you like, I'm just suggesting that we
> might not need read_current_timer after all.
> Will

Thanks, I should try patch v2. :-)

Chen Gang

Asianux Corporation
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at