tridentfb: Blade3D clock fixes

This patch fixes following problems:
- does not allow the m parameter to reach 0 as
  it locks the graphics core (power cycle needed)
- for the newer chips (with new clock registers)
  does not allow of n / m ratio below 4 as it gives
  unstable image on the Blade3D core
- extend shift parameter (k) range  to 2 for the newer
  chips to cope with the n /m >= 4 limit at low resolution
  (bandwidth) modes
- prefer modes with higher n / m ratio (higher k values)
Signed-off-by: NKrzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/video/tridentfb.c

@@ -672,15 +672,16 @@ static void set_vclk(struct tridentfb_par *par, unsigned long freq)
 	unsigned long fi, d, di;
 	unsigned char best_m = 0, best_n = 0, best_k = 0;
 	unsigned char hi, lo;
+	unsigned char shift = !is_oldclock(par->chip_id) ? 2 : 1;
 
 	d = 20000;
-	for (k = 1; k >= 0; k--)
-		for (m = 0; m < 32; m++) {
-			n = 2 * (m + 2) - 8;
+	for (k = shift; k >= 0; k--)
+		for (m = 1; m < 32; m++) {
+			n = ((m + 2) << shift) - 8;
 			for (n = (n < 0 ? 0 : n); n < 122; n++) {
 				fi = ((14318l * (n + 8)) / (m + 2)) >> k;
 				di = abs(fi - freq);
-				if (di <= d) {
+				if (di < d || (di == d && k == best_k)) {
 					d = di;
 					best_n = n;
 					best_m = m;