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

[Scott Wood]

On Thu, Apr 17, 2008 at 04:52:35PM +0400, Anton Vorontsov wrote:
> Heh. Scott, think about it. You have single 16bit timer with variable
> frequency. To use it, you'd better know what exactly precision you need.

Why?  I know the timeout I need.

> Then you limited to u16 for the interval for this chosen precision.
> 
> Yes, you can implement this:
> 
> #define MAX_PRESCALER (256 * 256 * 16)
> 
> int gtm_reset_weird_behaving_utimer16(struct gtm_timer *tmr,
> 				      unsigned long long usec,
> 				      bool free_run)
> {
> 	int freq = 1000000;
> 	int min_hz2 = (tmr->gtm->freq / MAX_PRESCALER) << 1;
> 
> 	while (!(freq & 1) && !(usec & 1) && freq >= min_hz2) {
> 		freq >>= 1;
> 		usec >>= 1;
> 	}
> 
> 	if (usec > 0xffff)
> 		return -EINVAL;
> 
> 	return gtm_reset_ref_timer16(tmr, freq, (u16)usec, free_run);
> }

Try something like this:

int gtm_reset_sane_behaving_timer(struct gtm_timer *tmr,
                                  u64 usec, bool free_run)
{
	int freq = 1000000;
	int min_hz2 = (tmr->gtm->freq / MAX_PRESCALER) << 1;

	while (usec > 0xffff && freq >= min_hz2) {
		freq >>= 1;
		usec >>= 1;
	}

	if (usec > 0xffff)
		return -EINVAL;

	return gtm_reset_ref_timer16(tmr, freq, usec, free_run);
}

It could be made faster using cntlzw.

-Scott