drm/mgag200: fix G200ER pll picking algorithm
The original code was misported from the X driver,
a) an int went to unsigned int, breaking the downward counting testm code
b) the port did the vco/computed clock bits completely wrong.
This fixes an infinite loop on modprobe on some Dell servers with the G200ER
chipset variant.
Found in internal testing.
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
index a4d7c50..b69642d 100644
--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -468,10 +468,11 @@
{
unsigned int vcomax, vcomin, pllreffreq;
unsigned int delta, tmpdelta;
- unsigned int testr, testn, testm, testo;
+ int testr, testn, testm, testo;
unsigned int p, m, n;
- unsigned int computed;
+ unsigned int computed, vco;
int tmp;
+ const unsigned int m_div_val[] = { 1, 2, 4, 8 };
m = n = p = 0;
vcomax = 1488000;
@@ -490,12 +491,13 @@
if (delta == 0)
break;
for (testo = 5; testo < 33; testo++) {
- computed = pllreffreq * (testn + 1) /
+ vco = pllreffreq * (testn + 1) /
(testr + 1);
- if (computed < vcomin)
+ if (vco < vcomin)
continue;
- if (computed > vcomax)
+ if (vco > vcomax)
continue;
+ computed = vco / (m_div_val[testm] * (testo + 1));
if (computed > clock)
tmpdelta = computed - clock;
else
