drm/i915: fix haswell linetime watermarks calculation

Move the "*8"  calculation to the left side so we don't propagate
rounding errors. Also use DIV_ROUND_CLOSEST because that's what the
spec says we need to do.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 198d9c9ada683d99efafa2cb652cce776292f2b7..2c406ddc6354943e865f760410feec0153ca3189 100644 (file)
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2093,7 +2093,7 @@ haswell_update_linetime_wm(struct drm_device *dev, struct drm_crtc *crtc)
         * row at the given clock rate, multiplied by 8.
         * */
        temp |= PIPE_WM_LINETIME_TIME(
-               ((mode->htotal * 1000) / mode->clock) * 8);
+               DIV_ROUND_CLOSEST(mode->htotal * 1000 * 8, mode->clock));
 
        /* IPS watermarks are only used by pipe A, and are ignored by
         * pipes B and C.  They are calculated similarly to the common