[Intel-gfx] [PATCH 03/12] drm/i915: Simplify VLV drain latency computation

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

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 at virtuousgeek.org>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 0f0281a..d6c6c1b 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -727,12 +727,15 @@ 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;
 
-- 
2.0.5