drm/i915: Fix computation of last_adjustment for RPS autotuning

The issue is that by computing the last_adj value after applying the
clamping, we can end up with a bogus value for feeding into the next RPS
autotuning step.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -1095,21 +1095,20 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	pm_iir |= vlv_wa_c0_ei(dev_priv, pm_iir);
 
 	adj = dev_priv->rps.last_adj;
+	new_delay = dev_priv->rps.cur_freq;
 	if (pm_iir & GEN6_PM_RP_UP_THRESHOLD) {
 		if (adj > 0)
 			adj *= 2;
-		else {
-			/* CHV needs even encode values */
-			adj = IS_CHERRYVIEW(dev_priv->dev) ? 2 : 1;
-		}
-		new_delay = dev_priv->rps.cur_freq + adj;
-
+		else /* CHV needs even encode values */
+			adj = IS_CHERRYVIEW(dev_priv) ? 2 : 1;
 		/*
 		 * For better performance, jump directly
 		 * to RPe if we're below it.
 		 */
-		if (new_delay < dev_priv->rps.efficient_freq)
+		if (new_delay < dev_priv->rps.efficient_freq - adj) {
 			new_delay = dev_priv->rps.efficient_freq;
+			adj = 0;
+		}
 	} else if (pm_iir & GEN6_PM_RP_DOWN_TIMEOUT) {
 		if (dev_priv->rps.cur_freq > dev_priv->rps.efficient_freq)
 			new_delay = dev_priv->rps.efficient_freq;
@@ -1119,24 +1118,22 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	} else if (pm_iir & GEN6_PM_RP_DOWN_THRESHOLD) {
 		if (adj < 0)
 			adj *= 2;
-		else {
-			/* CHV needs even encode values */
-			adj = IS_CHERRYVIEW(dev_priv->dev) ? -2 : -1;
-		}
-		new_delay = dev_priv->rps.cur_freq + adj;
+		else /* CHV needs even encode values */
+			adj = IS_CHERRYVIEW(dev_priv) ? -2 : -1;
 	} else { /* unknown event */
-		new_delay = dev_priv->rps.cur_freq;
+		adj = 0;
 	}
 
+	dev_priv->rps.last_adj = adj;
+
 	/* sysfs frequency interfaces may have snuck in while servicing the
 	 * interrupt
 	 */
+	new_delay += adj;
 	new_delay = clamp_t(int, new_delay,
 			    dev_priv->rps.min_freq_softlimit,
 			    dev_priv->rps.max_freq_softlimit);
 
-	dev_priv->rps.last_adj = new_delay - dev_priv->rps.cur_freq;
-
 	intel_set_rps(dev_priv->dev, new_delay);
 
 	mutex_unlock(&dev_priv->rps.hw_lock);