drm/tegra: dc: Balance IOMMU group refcounting

Remove unneeded iommu_group_get() and add missing iommu_group_put(),
correcting IOMMU group refcount. This is a minor correction / cleanup that
doesn't really fix anything because Tegra's IOMMU driver are built-in and
hence groups refcounting can't hold IOMMU driver from unloading.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dc.c

@@ -1826,7 +1826,6 @@ static irqreturn_t tegra_dc_irq(int irq, void *data)
 static int tegra_dc_init(struct host1x_client *client)
 {
 	struct drm_device *drm = dev_get_drvdata(client->parent);
-	struct iommu_group *group = iommu_group_get(client->dev);
 	unsigned long flags = HOST1X_SYNCPT_CLIENT_MANAGED;
 	struct tegra_dc *dc = host1x_client_to_dc(client);
 	struct tegra_drm *tegra = drm->dev_private;
@@ -1838,20 +1837,21 @@ static int tegra_dc_init(struct host1x_client *client)
 	if (!dc->syncpt)
 		dev_warn(dc->dev, "failed to allocate syncpoint\n");
 
-	if (group && tegra->domain) {
-		if (group != tegra->group) {
-			err = iommu_attach_group(tegra->domain, group);
+	if (tegra->domain) {
+		dc->group = iommu_group_get(client->dev);
+
+		if (dc->group && dc->group != tegra->group) {
+			err = iommu_attach_group(tegra->domain, dc->group);
 			if (err < 0) {
 				dev_err(dc->dev,
 					"failed to attach to domain: %d\n",
 					err);
+				iommu_group_put(dc->group);
 				return err;
 			}
 
-			tegra->group = group;
+			tegra->group = dc->group;
 		}
-
-		dc->domain = tegra->domain;
 	}
 
 	if (dc->soc->wgrps)
@@ -1916,13 +1916,13 @@ static int tegra_dc_init(struct host1x_client *client)
 	if (!IS_ERR(primary))
 		drm_plane_cleanup(primary);
 
-	if (group && dc->domain) {
-		if (group == tegra->group) {
-			iommu_detach_group(dc->domain, group);
+	if (dc->group) {
+		if (dc->group == tegra->group) {
+			iommu_detach_group(tegra->domain, dc->group);
 			tegra->group = NULL;
 		}
 
-		dc->domain = NULL;
+		iommu_group_put(dc->group);
 	}
 
 	return err;
@@ -1931,7 +1931,6 @@ static int tegra_dc_init(struct host1x_client *client)
 static int tegra_dc_exit(struct host1x_client *client)
 {
 	struct drm_device *drm = dev_get_drvdata(client->parent);
-	struct iommu_group *group = iommu_group_get(client->dev);
 	struct tegra_dc *dc = host1x_client_to_dc(client);
 	struct tegra_drm *tegra = drm->dev_private;
 	int err;
@@ -1944,13 +1943,13 @@ static int tegra_dc_exit(struct host1x_client *client)
 		return err;
 	}
 
-	if (group && dc->domain) {
-		if (group == tegra->group) {
-			iommu_detach_group(dc->domain, group);
+	if (dc->group) {
+		if (dc->group == tegra->group) {
+			iommu_detach_group(tegra->domain, dc->group);
 			tegra->group = NULL;
 		}
 
-		dc->domain = NULL;
+		iommu_group_put(dc->group);
 	}
 
 	host1x_syncpt_free(dc->syncpt);

drivers/gpu/drm/tegra/dc.h

@@ -92,7 +92,7 @@ struct tegra_dc {
 
 	const struct tegra_dc_soc_info *soc;
 
-	struct iommu_domain *domain;
+	struct iommu_group *group;
 };
 
 static inline struct tegra_dc *