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drm/mgag200: fix G200ER pll picking algorithm

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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>
This commit is contained in:
Dave Airlie 2012-08-09 15:00:15 +10:00
parent f7b83b908f
commit 9830605d4c
1 changed files with 7 additions and 5 deletions
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12
drivers/gpu/drm/mgag200/mgag200_mode.c
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@ -468,10 +468,11 @@ static int mga_g200er_set_plls(struct mga_device *mdev, long clock)
{
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 @@ static int mga_g200er_set_plls(struct mga_device *mdev, long clock)
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