drm/i915: debugfs interface for forcewake reference count

forcewake is controlled by the open and close of the debugfs file. This
assures that buggy applications cannot cause the GT to stay on forever.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1217,6 +1217,18 @@ static int i915_context_status(struct seq_file *m, void *unused)
 	return 0;
 }
 
+static int i915_gen6_forcewake_count_info(struct seq_file *m, void *data)
+{
+	struct drm_info_node *node = (struct drm_info_node *) m->private;
+	struct drm_device *dev = node->minor->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	seq_printf(m, "forcewake count = %d\n",
+		   atomic_read(&dev_priv->forcewake_count));
+
+	return 0;
+}
+
 static int
 i915_wedged_open(struct inode *inode,
 		 struct file *filp)
@@ -1319,6 +1331,67 @@ static int i915_wedged_create(struct dentry *root, struct drm_minor *minor)
 	return drm_add_fake_info_node(minor, ent, &i915_wedged_fops);
 }
 
+static int i915_forcewake_open(struct inode *inode, struct file *file)
+{
+	struct drm_device *dev = inode->i_private;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	int ret;
+
+	if (!IS_GEN6(dev))
+		return 0;
+
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	if (ret)
+		return ret;
+	gen6_gt_force_wake_get(dev_priv);
+	mutex_unlock(&dev->struct_mutex);
+
+	return 0;
+}
+
+int i915_forcewake_release(struct inode *inode, struct file *file)
+{
+	struct drm_device *dev = inode->i_private;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (!IS_GEN6(dev))
+		return 0;
+
+	/*
+	 * It's bad that we can potentially hang userspace if struct_mutex gets
+	 * forever stuck.  However, if we cannot acquire this lock it means that
+	 * almost certainly the driver has hung, is not unload-able. Therefore
+	 * hanging here is probably a minor inconvenience not to be seen my
+	 * almost every user.
+	 */
+	mutex_lock(&dev->struct_mutex);
+	gen6_gt_force_wake_put(dev_priv);
+	mutex_unlock(&dev->struct_mutex);
+
+	return 0;
+}
+
+static const struct file_operations i915_forcewake_fops = {
+	.owner = THIS_MODULE,
+	.open = i915_forcewake_open,
+	.release = i915_forcewake_release,
+};
+
+static int i915_forcewake_create(struct dentry *root, struct drm_minor *minor)
+{
+	struct drm_device *dev = minor->dev;
+	struct dentry *ent;
+
+	ent = debugfs_create_file("i915_forcewake_user",
+				  S_IRWXU,
+				  root, dev,
+				  &i915_forcewake_fops);
+	if (IS_ERR(ent))
+		return PTR_ERR(ent);
+
+	return 0;
+}
+
 static struct drm_info_list i915_debugfs_list[] = {
 	{"i915_capabilities", i915_capabilities, 0},
 	{"i915_gem_objects", i915_gem_object_info, 0},
@@ -1356,6 +1429,7 @@ static struct drm_info_list i915_debugfs_list[] = {
 	{"i915_opregion", i915_opregion, 0},
 	{"i915_gem_framebuffer", i915_gem_framebuffer_info, 0},
 	{"i915_context_status", i915_context_status, 0},
+	{"i915_gen6_forcewake_count", i915_gen6_forcewake_count_info, 0},
 };
 #define I915_DEBUGFS_ENTRIES ARRAY_SIZE(i915_debugfs_list)
 
@@ -1367,6 +1441,10 @@ int i915_debugfs_init(struct drm_minor *minor)
 	if (ret)
 		return ret;
 
+	ret = i915_forcewake_create(minor->debugfs_root, minor);
+	if (ret)
+		return ret;
+
 	return drm_debugfs_create_files(i915_debugfs_list,
 					I915_DEBUGFS_ENTRIES,
 					minor->debugfs_root, minor);
@@ -1376,6 +1454,8 @@ void i915_debugfs_cleanup(struct drm_minor *minor)
 {
 	drm_debugfs_remove_files(i915_debugfs_list,
 				 I915_DEBUGFS_ENTRIES, minor);
+	drm_debugfs_remove_files((struct drm_info_list *) &i915_forcewake_fops,
+				 1, minor);
 	drm_debugfs_remove_files((struct drm_info_list *) &i915_wedged_fops,
 				 1, minor);
 }