drm/nva3: fix overflow in fixed point math used for pll calculation
[linux-2.6.git] / drivers / gpu / drm / nouveau / nv50_calc.c
index 2cdc2bf..de81151 100644 (file)
@@ -51,24 +51,28 @@ nv50_calc_pll2(struct drm_device *dev, struct pll_lims *pll, int clk,
               int *N, int *fN, int *M, int *P)
 {
        fixed20_12 fb_div, a, b;
+       u32 refclk = pll->refclk / 10;
+       u32 max_vco_freq = pll->vco1.maxfreq / 10;
+       u32 max_vco_inputfreq = pll->vco1.max_inputfreq / 10;
+       clk /= 10;
 
-       *P = pll->vco1.maxfreq / clk;
+       *P = max_vco_freq / clk;
        if (*P > pll->max_p)
                *P = pll->max_p;
        if (*P < pll->min_p)
                *P = pll->min_p;
 
-       /* *M = ceil(refclk / pll->vco.max_inputfreq); */
-       a.full = dfixed_const(pll->refclk);
-       b.full = dfixed_const(pll->vco1.max_inputfreq);
+       /* *M = floor((refclk + max_vco_inputfreq) / max_vco_inputfreq); */
+       a.full = dfixed_const(refclk + max_vco_inputfreq);
+       b.full = dfixed_const(max_vco_inputfreq);
        a.full = dfixed_div(a, b);
-       a.full = dfixed_ceil(a);
+       a.full = dfixed_floor(a);
        *M = dfixed_trunc(a);
 
        /* fb_div = (vco * *M) / refclk; */
        fb_div.full = dfixed_const(clk * *P);
        fb_div.full = dfixed_mul(fb_div, a);
-       a.full = dfixed_const(pll->refclk);
+       a.full = dfixed_const(refclk);
        fb_div.full = dfixed_div(fb_div, a);
 
        /* *N = floor(fb_div); */