drm/i915: Error checks in gen6_set_rps

With the new "standardized" sysfs interfaces we need to be a bit more
careful about setting the RPS values.

Because the sysfs code and the rps workqueue can run at the same time,
if the sysfs setter wins the race to the mutex, the workqueue can come
in and set a value which is out of range (ie. we're no longer protecting
by RPINTLIM).

I was not able to actually make this error occur in testing.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -382,7 +382,13 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	else
 		new_delay = dev_priv->rps.cur_delay - 1;
 
-	gen6_set_rps(dev_priv->dev, new_delay);
+	/* sysfs frequency interfaces may have snuck in while servicing the
+	 * interrupt
+	 */
+	if (!(new_delay > dev_priv->rps.max_delay ||
+	      new_delay < dev_priv->rps.min_delay)) {
+		gen6_set_rps(dev_priv->dev, new_delay);
+	}
 
 	mutex_unlock(&dev_priv->dev->struct_mutex);
 }

drivers/gpu/drm/i915/intel_pm.c

@@ -2324,6 +2324,8 @@ void gen6_set_rps(struct drm_device *dev, u8 val)
 	u32 limits = gen6_rps_limits(dev_priv, &val);
 
 	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+	WARN_ON(val > dev_priv->rps.max_delay);
+	WARN_ON(val < dev_priv->rps.min_delay);
 
 	if (val == dev_priv->rps.cur_delay)
 		return;