[Intel-gfx] [PATCH 2/2]drm/i915: Use?best PLL timing values for G4X chipsets

[Wang, Zhenyu Z]

On 2009.03.12 10:20:33 +0800, Fu Michael wrote:
> Zhenyu Wang wrote:
> > On 2009.03.10 21:00:25 +0800, Ma Ling wrote:
> >   
> >> +
> >> +	memset (best_clock, 0, sizeof (*best_clock));
> >> +	max_n = limit->n.max;
> >> +	/* based on hardware requriment prefer smaller n to precision */
> >> +	for (clock.n = limit->n.min; clock.n <= max_n; clock.n++) {
> >> +		/* based on hardware requirment prefere larger m1,m2, p1 */
> >> +		for (clock.m1 = limit->m1.max;
> >> +		     clock.m1 >= limit->m1.min; clock.m1--) {
> >> +			for (clock.m2 = limit->m2.max;
> >> +			     clock.m2 >= limit->m2.min; clock.m2--) {
> >> +				for (clock.p1 = limit->p1.max;
> >> +				     clock.p1 >= limit->p1.min; clock.p1--) {
> >> +					int this_err;
> >> +
> >> +					intel_clock (refclk, &clock);
> >> +					if (!intel_PLL_is_valid(crtc, &clock))
> >> +						continue;
> >> +					this_err = abs(clock.dot - target) ;
> >> +					if (this_err < err_most) {
> >> +						*best_clock = clock;
> >> +						err_most = this_err;
> >> +						/*chose smaller n*/
> >> +						max_n = clock.n;
> >> +						found = true;
> >>     
> >
> > If we should prefer larger m1,m2,p1, why not exit the cycle here and return? 
> > Here we still try to look for the smallest error for target but might not be preferred
> > largest m1,m2,p1?
> >   
> precision override m1,m2,p1 ( if a smaller m1,m2,p1 can get even better 
> precision, we go with smaller combination )
> N override precision ( if a bigger N can get even better precision in 
> the math, we still go with smaller N )
> 

ok, could we have some comments for this reason? Thanks.

> > And is it possible if no clock can be found that meets the error precision of target?
> > Should we guard for that case?
> >
> > And how about your test result on g4x with KMS?
> >
> >   
> 
> 

-- 
Open Source Technology Center, Intel ltd.

$gpg --keyserver wwwkeys.pgp.net --recv-keys 4D781827
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 197 bytes
Desc: Digital signature
URL: <http://lists.freedesktop.org/archives/intel-gfx/attachments/20090312/4c70e70a/attachment.sig>