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Subject[ 04/46] drm/mgag200: fix G200ER pll picking algorithm
Date
From: Greg KH <gregkh@linuxfoundation.org>

3.5-stable review patch. If anyone has any objections, please let me know.

------------------

From: Dave Airlie <airlied@gmail.com>

commit 9830605d4c070b16ec5c24a75503877cc7698409 upstream.

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.

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

---
drivers/gpu/drm/mgag200/mgag200_mode.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/mgag200/mgag200_mode.c
+++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
@@ -468,10 +468,11 @@ static int mga_g200er_set_plls(struct mg
{
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 mg
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



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