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: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/video/tridentfb.c b/drivers/video/tridentfb.c
index 138140bdb495..854e2e5af582 100644
--- a/drivers/video/tridentfb.c
+++ b/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;