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Commit 9830605d authored by Dave Airlie's avatar Dave Airlie
Browse files

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: default avatarDave Airlie <airlied@redhat.com>
parent f7b83b90

drivers/gpu/drm/mgag200/mgag200_mode.c

+7 −5
Original line number Diff line number Diff line
@@ -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