Re: [PATCH v2 05/14] drm/i915: Rewrite vlv_find_best_dpll()

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

ville.syrjala@linux.intel.com writes:

> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Rewrite vlv_find_best_dpll() to use intel_clock_t rather than
> an army of local variables.
>
> Also extract the code to calculate the derived values into
> vlv_clock().
>
> v2: Split up the earlier fixes, extract vlv_clock()
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 72 ++++++++++++++++--------------------
>  1 file changed, 31 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index f646fea..c5f0794 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -438,6 +438,14 @@ static void i9xx_clock(int refclk, intel_clock_t *clock)
>  	clock->dot = clock->vco / clock->p;
>  }
>  
> +static void vlv_clock(int refclk, intel_clock_t *clock)
> +{
> +	clock->m = clock->m1 * clock->m2;
> +	clock->p = clock->p1 * clock->p2;
> +	clock->vco = refclk * clock->m / clock->n;
> +	clock->dot = clock->vco / clock->p;
> +}
> +
>  /**
>   * Returns whether any output on the specified pipe is of the specified type
>   */
> @@ -670,66 +678,48 @@ vlv_find_best_dpll(const intel_limit_t *limit, struct drm_crtc *crtc,
>  		   int target, int refclk, intel_clock_t *match_clock,
>  		   intel_clock_t *best_clock)
>  {
> -	u32 p1, p2, m1, m2, vco, bestn, bestm1, bestm2, bestp1, bestp2;
> -	u32 m, n, fastclk;
> -	u32 updrate, minupdate, p;
> +	intel_clock_t clock;
> +	u32 minupdate = 19200;
>  	unsigned int bestppm = 1000000;
> -	int dotclk, flag;
>  
> -	flag = 0;
> -	dotclk = target * 1000;
> -	fastclk = dotclk / (2*100);
> -	updrate = 0;
> -	minupdate = 19200;
> -	n = p = p1 = p2 = m = m1 = m2 = vco = bestn = 0;
> -	bestm1 = bestm2 = bestp1 = bestp2 = 0;
> +	target *= 5; /* fast clock */
>  
>  	/* based on hardware requirement, prefer smaller n to precision */
> -	for (n = limit->n.min; n <= ((refclk) / minupdate); n++) {
> -		updrate = refclk / n;
> -		for (p1 = limit->p1.max; p1 > limit->p1.min; p1--) {
> -			for (p2 = limit->p2.p2_fast+1; p2 > 0; p2--) {
> -				if (p2 > 10)
> -					p2 = p2 - 1;
> -				p = p1 * p2;
> +	for (clock.n = limit->n.min; clock.n <= ((refclk) / minupdate); clock.n++) {
> +		for (clock.p1 = limit->p1.max; clock.p1 > limit->p1.min; clock.p1--) {
> +			for (clock.p2 = limit->p2.p2_fast+1; clock.p2 > 0; clock.p2--) {
> +				if (clock.p2 > 10)
> +					clock.p2--;
> +				clock.p = clock.p1 * clock.p2;
>  				/* based on hardware requirement, prefer bigger m1,m2 values */
> -				for (m1 = limit->m1.min; m1 <= limit->m1.max; m1++) {
> +				for (clock.m1 = limit->m1.min; clock.m1 <= limit->m1.max; clock.m1++) {
>  					unsigned int ppm, diff;
>  
> -					m2 = DIV_ROUND_CLOSEST(fastclk * p * n, refclk * m1);
> -					m = m1 * m2;
> -					vco = updrate * m;
> +					clock.m2 = DIV_ROUND_CLOSEST(target * clock.p * clock.n,
> +								     refclk * clock.m1);
>  
> -					if (vco < limit->vco.min || vco >= limit->vco.max)
> +					vlv_clock(refclk, &clock);
> +
> +					if (clock.vco < limit->vco.min ||
> +					    clock.vco >= limit->vco.max)
>  						continue;
>  
> -					diff = abs(vco / p - fastclk);
> -					ppm = div_u64(1000000ULL * diff, fastclk);
> -					if (ppm < 100 && ((p1 * p2) > (bestp1 * bestp2))) {
> +					diff = abs(clock.dot - target);
> +					ppm = div_u64(1000000ULL * diff, target);
> +
> +					if (ppm < 100 && clock.p > best_clock->p) {

best_clock needs to be initialized or you end up comparing against
bytes from stack on first hitting here.

>  						bestppm = 0;
> -						flag = 1;
> +						*best_clock = clock;
>  					}
> +
>  					if (bestppm >= 10 && ppm < bestppm - 10) {
>  						bestppm = ppm;
> -						flag = 1;
> -					}
> -					if (flag) {
> -						bestn = n;
> -						bestm1 = m1;
> -						bestm2 = m2;
> -						bestp1 = p1;
> -						bestp2 = p2;
> -						flag = 0;
> +						*best_clock = clock;
>  					}
>  				}
>  			}
>  		}
>  	}
> -	best_clock->n = bestn;
> -	best_clock->m1 = bestm1;
> -	best_clock->m2 = bestm2;
> -	best_clock->p1 = bestp1;
> -	best_clock->p2 = bestp2;
>  
>  	return true;
>  }
> -- 
> 1.8.1.5
>
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