diff options
Diffstat (limited to 'drivers/video/tdfxfb.c')
| -rw-r--r-- | drivers/video/tdfxfb.c | 43 |
1 files changed, 31 insertions, 12 deletions
diff --git a/drivers/video/tdfxfb.c b/drivers/video/tdfxfb.c index c34ba39..c8b0be2 100644 --- a/drivers/video/tdfxfb.c +++ b/drivers/video/tdfxfb.c @@ -317,30 +317,49 @@ static inline void do_setpalentry(struct tdfx_par *par, unsigned regno, u32 c) static u32 do_calc_pll(int freq, int* freq_out) { - int m, n, k, best_m, best_n, best_k, f_cur, best_error; + int m, n, k, best_m, best_n, best_k, best_error; int fref = 14318; - /* this really could be done with more intelligence -- - 255*63*4 = 64260 iterations is silly */ best_error = freq; best_n = best_m = best_k = 0; - for (n = 1; n < 256; n++) { - for (m = 1; m < 64; m++) { - for (k = 0; k < 4; k++) { - f_cur = fref*(n + 2)/(m + 2)/(1 << k); - if (abs(f_cur - freq) < best_error) { - best_error = abs(f_cur-freq); - best_n = n; - best_m = m; - best_k = k; + + for (k = 3; k >= 0; k--) { + for (m = 63; m >= 0; m--) { + /* + * Estimate value of n that produces target frequency + * with current m and k + */ + int n_estimated = (freq * (m + 2) * (1 << k) / fref) - 2; + + /* Search neighborhood of estimated n */ + for (n = max(0, n_estimated - 1); + n <= min(255, n_estimated + 1); n++) { + /* + * Calculate PLL freqency with current m, k and + * estimated n + */ + int f = fref * (n + 2) / (m + 2) / (1 << k); + int error = abs (f - freq); + + /* + * If this is the closest we've come to the + * target frequency then remember n, m and k + */ + if (error < best_error) { + best_error = error; + best_n = n; + best_m = m; + best_k = k; } } } } + n = best_n; m = best_m; k = best_k; *freq_out = fref*(n + 2)/(m + 2)/(1 << k); + return (n << 8) | (m << 2) | k; } |
