[RFC 1/2] AT91: Support SAM9260 and SAM9G20-based boards in the same kernel image

[gilles.chanteperdrix@xenomai.org (Gilles Chanteperdrix)]

Russell King - ARM Linux wrote:
> On Tue, Jan 18, 2011 at 04:00:30PM +0100, Jean-Christophe PLAGNIOL-VILLARD wrote:
>> this idea is to do not have CONFIG_ARCH_AT91SAM9G20 anymore only 9260
>>
>> and detect it
>>
>> but the man issue is the CLOCK_TICK_RATE which is different between both of
>> them except if we use a common one for those soc or the sam9/11 we could not
>> put them in the same kernel
> 
> If you switch to clocksource/clockevents, then I think CLOCK_TICK_RATE
> is irrelevant as time advances according to the interval measured by
> the previous and current clocksource read, rather than 1/HZ intervals.
> 
> However, I'm never happy to say "just set CLOCK_TICK_RATE to some random
> value that's a multiple of HZ" because I can't convince myself that these
> don't have any effect when using clocksources.  The list of symbols which
> depend on CLOCK_TICK_RATE are:
> 
> ACTHZ
> LATCH
> TICK_NSEC
> TICK_USEC_TO_NSEC
> LOW_RES_NSEC
> MONOTONIC_RES_NSEC
> NSEC_PER_JIFFY
> KTIME_LOW_RES
> 
> and if you grep for those outside of arch/, you find them being used in
> a fair amount of code under kernel/, as well as the odd driver here and
> there.

at91rm9200_time.c even seems to use LATCH, even though the clockevent
frequency is not explicitly set to CLOCK_TICK_RATE.

-- 
                                                                Gilles.