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

[Anton Vorontsov <avorontsov@ru.mvista.com>]

On Tue, May 20, 2008 at 06:32:34PM +0400, Anton Vorontsov wrote:
> On Tue, May 20, 2008 at 09:20:50AM -0500, Kumar Gala wrote:
> >>>>> 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)?
> 
> We're always prescale [to 1000000 MHz for usec precision].

-MHz
+Hz

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
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