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path: root/drivers/video/tdfxfb.c
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Diffstat (limited to 'drivers/video/tdfxfb.c')
-rw-r--r--drivers/video/tdfxfb.c43
1 files changed, 31 insertions, 12 deletions
diff --git a/drivers/video/tdfxfb.c b/drivers/video/tdfxfb.c
index c34ba39b6f7e..c8b0be2d8715 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;
}