drm/mgag200: Bug fix: Modified pll algorithm for EH project

commit 260b3f1291a75a580d22ce8bfb1499c617272716 upstream.

While testing the mgag200 kms driver on the HP ProLiant Gen8, a
bug was seen.  Once the bootloader would load the selected kernel,
the screen would go black.  At first it was assumed that the
mgag200 kms driver was hanging.  But after setting up the grub
serial output, it was seen that the driver was being loaded
properly.  After trying serval monitors, one finaly displayed
the message "Frequency Out of Range".  By comparing the kms pll
algorithm with the previous mgag200 xorg driver pll algorithm,
discrepencies were found.  Once the kms pll algorithm was
modified, the expected pll values were produced.  This fix was
tested on several monitors of varying native resolutions.

Signed-off-by: Julia Lemire <jlemire@matrox.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index d3d99a28ddef770d78525cd2e32786f40f047084..4f50c402ee9e0db19ba7f7ccde5ec1429f639a2b 100644 (file)
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -382,19 +382,19 @@ static int mga_g200eh_set_plls(struct mga_device *mdev, long clock)
        m = n = p = 0;
        vcomax = 800000;
        vcomin = 400000;
-       pllreffreq = 3333;
+       pllreffreq = 33333;
 
        delta = 0xffffffff;
        permitteddelta = clock * 5 / 1000;
 
-       for (testp = 16; testp > 0; testp--) {
+       for (testp = 16; testp > 0; testp >>= 1) {
                if (clock * testp > vcomax)
                        continue;
                if (clock * testp < vcomin)
                        continue;
 
                for (testm = 1; testm < 33; testm++) {
-                       for (testn = 1; testn < 257; testn++) {
+                       for (testn = 17; testn < 257; testn++) {
                                computed = (pllreffreq * testn) /
                                        (testm * testp);
                                if (computed > clock)
@@ -404,11 +404,11 @@ static int mga_g200eh_set_plls(struct mga_device *mdev, long clock)
                                if (tmpdelta < delta) {
                                        delta = tmpdelta;
                                        n = testn - 1;
-                                       m = (testm - 1) | ((n >> 1) & 0x80);
+                                       m = (testm - 1);
                                        p = testp - 1;
                                }
                                if ((clock * testp) >= 600000)
-                                       p |= 80;
+                                       p |= 0x80;
                        }
                }
        }