On Mon, Sep 23, 2013 at 09:03:10PM +0300, ville.syrj...@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrj...@linux.intel.com>
>
> vlv_find_best_dpll() has several integer over/underflow issues,
> includes a hand rolled DIV_ROUND_CLOSEST(), has a boat load of
> variables, some slightly weird math, and it doesn't look very
> nice either.
>
> Rather than try to deal with each issue separately I just decided
> to rewrite the function a bit.
>
> WARNING: Entirely untested
>
> Signed-off-by: Ville Syrjälä <ville.syrj...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 94
> +++++++++++++++---------------------
> 1 file changed, 40 insertions(+), 54 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c
> b/drivers/gpu/drm/i915/intel_display.c
> index 3b06250..f89fb12 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -670,65 +670,51 @@ 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;
> - unsigned long bestppm, ppm, absppm;
> - int dotclk, flag;
> -
> - flag = 0;
> - dotclk = target * 1000;
> - bestppm = 1000000;
> - ppm = absppm = 0;
> - fastclk = dotclk / (2*100);
> - updrate = 0;
> - minupdate = 19200;
> - n = p = p1 = p2 = m = m1 = m2 = vco = bestn = 0;
> - bestm1 = bestm2 = bestp1 = bestp2 = 0;
> + intel_clock_t clock = {
> + .dot = target * 5, /* fast clock */
> + };
> + unsigned int bestppm = 1000000;
> + /* min update 19.2 MHz */
> + int max_n = min(limit->n.max, refclk / 19200);
>
> /* 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;
> - /* based on hardware requirement, prefer bigger
> m1,m2 values */
> - for (m1 = limit->m1.min; m1 <= limit->m1.max;
> m1++) {
> - m2 = (((2*(fastclk * p * n / m1 )) +
> - refclk) / (2*refclk));
> - m = m1 * m2;
> - vco = updrate * m;
> - if (vco >= limit->vco.min && vco <
> limit->vco.max) {
> - ppm = 1000000 * ((vco / p) -
> fastclk) / fastclk;
> - absppm = (ppm > 0) ? ppm :
> (-ppm);
> - if (absppm < 100 && ((p1 * p2)
> > (bestp1 * bestp2))) {
> - bestppm = 0;
> - flag = 1;
> - }
> - if (absppm < bestppm - 10) {
> - bestppm = absppm;
> - flag = 1;
> - }
> - if (flag) {
> - bestn = n;
> - bestm1 = m1;
> - bestm2 = m2;
> - bestp1 = p1;
> - bestp2 = p2;
> - flag = 0;
> - }
> - }
> - }
> + for (clock.n = limit->n.min; clock.n <= max_n; 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--) {
I think that's going to upset the coding style police ;-) I guess it would
be simple to extract a vlv_compute_clock like we have for pnv/i9xx that's
both used here and in the get_clock code from Jesse.
-Daniel
> + if (clock.p2 > 10)
> + clock.p2--;
> + clock.p = clock.p1 * clock.p2;
> +
> + /* based on hardware requirement, prefer bigger m1,m2 values */
> + for (clock.m1 = limit->m1.min; clock.m1 <= limit->m1.max;
> clock.m1++) {
> + unsigned int ppm, diff;
> +
> + clock.m2 = DIV_ROUND_CLOSEST(clock.dot * clock.p *
> clock.n,
> + clock.m1 * refclk);
> + clock.m = clock.m1 * clock.m2;
> +
> + clock.vco = refclk * clock.m / clock.n;
> +
> + if (clock.vco < limit->vco.min ||
> + clock.vco >= limit->vco.max)
> + continue;
> +
> + diff = abs(clock.vco / clock.p - clock.dot);
> + ppm = div_u64(1000000ULL * diff, clock.dot);
> +
> + if (ppm < 100 && clock.p > best_clock->p) {
> + bestppm = 0;
> + *best_clock = clock;
> + }
> +
> + if (ppm + 10 < bestppm) {
> + bestppm = ppm;
> + *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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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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