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authorRichard Drummond <evilrich@rcdrummond.net>2005-05-01 08:59:24 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-05-01 08:59:24 -0700
commit0fbe9cafff72799700713e6a9d5a4ec7191e8d19 (patch)
treebd0c48641b7281926346465ab7c8f7fae05bbeaf /drivers/video/tdfxfb.c
parent7c2f891cb64b0b9c8d389da97c221ee4288f1307 (diff)
downloadlinux-0fbe9cafff72799700713e6a9d5a4ec7191e8d19.tar.gz
[PATCH] Better PLL frequency matching for tdfxfb driver
Improve the PLL frequency matching in the tdfxfb driver. Instead of requiring 64260 iterations to obtain the closest supported PLL frequency, this code does it with the same degree of accuracy in at most 768 iterations. Signed-off-by: Richard Drummond <evilrich@rcdrummond.net> Cc: <linux-fbdev-devel@lists.sourceforge.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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 c34ba39b6f7..c8b0be2d871 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;
}