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 -- 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/
