[PATCH 1/7] [POWERPC] sysdev: implement FSL GTM support

Kumar Gala galak at kernel.crashing.org
Wed May 21 00:20:50 EST 2008

>>>> This is explained in the .c file with a kernel doc. Basically the
>>> difference is that timer16 could silently crop the precision, while
>>> utimer16 could not thus explicitly accepts u16 argument (max. timer
>>> interval with usec precision fits in u16).
>> Maybe I'm confused what the utility is of cropping the precision in  
>> this
>> way is.  I'd also say that _timer16 is poorly named to convey the
>> behavior. I'm not sure what to call it because I still dont get  
>> exactly
>> why you'd want the precision cropped.
> Precision matters for FHCI-like drivers, when driver, for example,
> schedule transactions via the GTM timers, and there timings matters
> a lot.
> Though, timer16 crops the precision _only_ if usecs > 65535, so FHCI
> _can_ still use the _timer16 (because FHCI does not request intervals
>> 65535). But I implemented two function because:
> 1. I think we don't need unnecessary stuff in the ISRs (this is weak
>   argument since I didn't measure the impact).
> 2. I wanted to make the API clear (seem to fail this undertaking :-),
>   which functions will behave exactly the way you asked it (utimer16),
>   and which functions will _silently_ crop the precision (timer16)
>   (if asked for 1001000 usecs, it will give you ~~1001000, depending
>   on the GTM frequency).

I'm fine w/having both. I think they are poorly named.  I'd also call  
them _set_timer but that's just me.

Maybe something w/the term _exact_ in the name.  Is it the case w/the  
precise form we'd have no prescaling (if so maybe a comment in the API  
about that would help clarity)?

- k

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