From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
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.syrjala@xxxxxxxxxxxxxxx>
---
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--) {
+ 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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