drm/i915: Simplify VLV drain latency computation

The current drain lantency computation relies on hardcoded limits to
determine when the to use the low vs. high precision multiplier.
Rewrite the code to use a more straightforward approach.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-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 cc3c2d9eb7f40dc9825d26e096cab82cf073b6ec..c198dbad3e8286f5b202228206891f4ef58d995e 100644 (file)
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -755,12 +755,15 @@ static bool vlv_compute_drain_latency(struct drm_crtc *crtc,
                return false;
 
        entries = DIV_ROUND_UP(clock, 1000) * pixel_size;
-       if (IS_CHERRYVIEW(dev))
-               *prec_mult = (entries > 32) ? 16 : 8;
-       else
-               *prec_mult = (entries > 128) ? 64 : 32;
+
+       *prec_mult = IS_CHERRYVIEW(dev) ? 16 : 64;
        *drain_latency = (64 * (*prec_mult) * 4) / entries;
 
+       if (*drain_latency > DRAIN_LATENCY_MASK) {
+               *prec_mult /= 2;
+               *drain_latency = (64 * (*prec_mult) * 4) / entries;
+       }
+
        if (*drain_latency > DRAIN_LATENCY_MASK)
                *drain_latency = DRAIN_LATENCY_MASK;