Re: [PATCH 6/8] [POWERPC] sysdev,qe_lib: implement FSL GTM support

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

On Thu, Apr 17, 2008 at 11:14:00AM -0500, Scott Wood wrote:
> Anton Vorontsov wrote:
>> This isn't a timer with usec precision! This is a timer that silently
>> crops precision as it wants to. Ahh, I see you dropped "u" prefix.
>
> It is a timer with usec precision, unless you ask for a timeout of more  
> than 65535 usec -- at which point the hardware can't provide usec 
> precision.
>
> And s/as it wants to/as it needs to/.
>
>> Well. I'm not going to use it anyway, so just give it some name you
>> prefer and I'll wrap it into the patch. Preferably, drop a line here with
>> kerneldoc for it, so I'll not have to document its drawbacks. :-)
>
> /**
>  * gtm_reset_timer16 - reset 16 bit timer with arbitrary precision
>  * @tmr: pointer to the gtm_timer structure obtained from gtm_get_timer
>  * @usec: timer interval in microseconds
>  * @reload: if set, the timer will reset upon expiry rather than
>  * continue running free.
>  *
>  * This function (re)sets the GTM timer so that it counts up to the
>  * requested interval value, and fires the interrupt when the value is
>  * reached.  This function will reduce the precision of the timer as
>  * needed in order for the requested timeout to fit in a 16-bit
>  * register.
>  */
> int gtm_reset_timer16(struct gtm_timer *tmr, unsigned long usec,
>                       bool reload)
> {
> 	...
> }

Thanks!

>>> It could be made faster using cntlzw.
>>
>> No need to cntlzw, there is fls() already.
>
> fls() uses cntlzw, does it not?  I was just too lazy to look up what  
> Linux calls it. :-)

Yup, I looked it up. ;-)

>> Though, here you'll need two because of u64.
>
> We can probably get away with 32 bits.
>
>> Btw, I hope you aware that single GTM timer running at 166MHz will give you
>> 6 minutes of sleep, maximum.
>
> Yes, but it's all we have on-chip that can do the job.
>
>> With cascaded timer you'll get much better
>> result of 310 days. Is that possible to use cascaded timer as a wakeup
>> event on 8313? 
>
> No, unfortunately.  Only timer4 can be a wakeup source, and when  
> cascaded, timer4 is the input to timer3, rather than the other way 
> around.

Ok, very well.

-- 
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2