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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
