drm/i915: fixup up debugfs rps state handling

- Take the dev->struct_mutex around access the corresponding state
  (and adjusting the rps hw state).
- Add an assert to gen6_set_rps to ensure we don't forget about this
  in the future.
- Don't set up the min/max_freq files if it doesn't apply to the hw.
  And do the same for the gen6+ cache sharing file while at it.

v2: Move the gen6+ checks into the read/write callbacks. Thanks to the
awesome drm midlayer we can't check that when registering the debugfs
files, because the driver is not yet fully set up, specifically the
->load callback hasn't run yet.

Oh how I despise this disaster ...

v3: Also add a WARN_ON(mutex_is_locked) in set_rps to check the
locking.

v4: Use mutex_lock_interruptible, suggested by Chris Wilson.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net> (for v2)
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1691,10 +1691,18 @@ i915_max_freq_read(struct file *filp,
 	struct drm_device *dev = filp->private_data;
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	char buf[80];
-	int len;
+	int len, ret;
+
+	if (!(IS_GEN6(dev) || IS_GEN7(dev)))
+		return -ENODEV;
+
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	if (ret)
+		return ret;
 
 	len = snprintf(buf, sizeof(buf),
 		       "max freq: %d\n", dev_priv->max_delay * 50);
+	mutex_unlock(&dev->struct_mutex);
 
 	if (len > sizeof(buf))
 		len = sizeof(buf);
@@ -1711,7 +1719,10 @@ i915_max_freq_write(struct file *filp,
 	struct drm_device *dev = filp->private_data;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	char buf[20];
-	int val = 1;
+	int val = 1, ret;
+
+	if (!(IS_GEN6(dev) || IS_GEN7(dev)))
+		return -ENODEV;
 
 	if (cnt > 0) {
 		if (cnt > sizeof(buf) - 1)
@@ -1726,12 +1737,17 @@ i915_max_freq_write(struct file *filp,
 
 	DRM_DEBUG_DRIVER("Manually setting max freq to %d\n", val);
 
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	if (ret)
+		return ret;
+
 	/*
 	 * Turbo will still be enabled, but won't go above the set value.
 	 */
 	dev_priv->max_delay = val / 50;
 
 	gen6_set_rps(dev, val / 50);
+	mutex_unlock(&dev->struct_mutex);
 
 	return cnt;
 }
@@ -1751,10 +1767,18 @@ i915_min_freq_read(struct file *filp, char __user *ubuf, size_t max,
 	struct drm_device *dev = filp->private_data;
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	char buf[80];
-	int len;
+	int len, ret;
+
+	if (!(IS_GEN6(dev) || IS_GEN7(dev)))
+		return -ENODEV;
+
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	if (ret)
+		return ret;
 
 	len = snprintf(buf, sizeof(buf),
 		       "min freq: %d\n", dev_priv->min_delay * 50);
+	mutex_unlock(&dev->struct_mutex);
 
 	if (len > sizeof(buf))
 		len = sizeof(buf);
@@ -1769,7 +1793,10 @@ i915_min_freq_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	struct drm_device *dev = filp->private_data;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	char buf[20];
-	int val = 1;
+	int val = 1, ret;
+
+	if (!(IS_GEN6(dev) || IS_GEN7(dev)))
+		return -ENODEV;
 
 	if (cnt > 0) {
 		if (cnt > sizeof(buf) - 1)
@@ -1784,12 +1811,17 @@ i915_min_freq_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 	DRM_DEBUG_DRIVER("Manually setting min freq to %d\n", val);
 
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	if (ret)
+		return ret;
+
 	/*
 	 * Turbo will still be enabled, but won't go below the set value.
 	 */
 	dev_priv->min_delay = val / 50;
 
 	gen6_set_rps(dev, val / 50);
+	mutex_unlock(&dev->struct_mutex);
 
 	return cnt;
 }
@@ -1814,6 +1846,9 @@ i915_cache_sharing_read(struct file *filp,
 	u32 snpcr;
 	int len;
 
+	if (!(IS_GEN6(dev) || IS_GEN7(dev)))
+		return -ENODEV;
+
 	mutex_lock(&dev_priv->dev->struct_mutex);
 	snpcr = I915_READ(GEN6_MBCUNIT_SNPCR);
 	mutex_unlock(&dev_priv->dev->struct_mutex);
@@ -1840,6 +1875,9 @@ i915_cache_sharing_write(struct file *filp,
 	u32 snpcr;
 	int val = 1;
 
+	if (!(IS_GEN6(dev) || IS_GEN7(dev)))
+		return -ENODEV;
+
 	if (cnt > 0) {
 		if (cnt > sizeof(buf) - 1)
 			return -EINVAL;
@@ -2044,6 +2082,7 @@ int i915_debugfs_init(struct drm_minor *minor)
 				  &i915_cache_sharing_fops);
 	if (ret)
 		return ret;
+
 	ret = i915_debugfs_create(minor->debugfs_root, minor,
 				  "i915_ring_stop",
 				  &i915_ring_stop_fops);

drivers/gpu/drm/i915/intel_pm.c

@@ -2300,6 +2300,8 @@ void gen6_set_rps(struct drm_device *dev, u8 val)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 limits = gen6_rps_limits(dev_priv, &val);
 
+	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+
 	if (val == dev_priv->cur_delay)
 		return;