drm/radeon/dce32+: use fractional fb dividers for high clocks

commit a02dc74b upstream.

Fixes flickering with some high res montiors.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: use pll->flags instead of radeon_crtc->pll_flags]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Weng Meiling <wengmeiling.weng@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -573,6 +573,8 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc,
 		/* use frac fb div on APUs */
 		if (ASIC_IS_DCE41(rdev) || ASIC_IS_DCE61(rdev))
 			pll->flags |= RADEON_PLL_USE_FRAC_FB_DIV;
+		if (ASIC_IS_DCE32(rdev) && mode->clock > 165000)
+			pll->flags |= RADEON_PLL_USE_FRAC_FB_DIV;
 	} else {
 		pll->flags |= RADEON_PLL_LEGACY;