drm/mediatek: Fix kobject put for component sub-drivers

In function mtk_drm_get_all_drm_priv(), this driver is incrementing
the refcount for the sub-drivers of mediatek-drm with a call to
device_find_child() when taking a reference to all of those child
devices.

When the component bind fails multiple times this results in a
refcount_t overflow, as the reference count is never decremented:
fix that by adding a call to put_device() for all of the mmsys
devices in a loop, in error cases of mtk_drm_bind() and in the
mtk_drm_unbind() callback.

Fixes: 1ef7ed4 ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
Reviewed-by: Chen-Yu Tsai <[email protected]>
Signed-off-by: AngeloGioacchino Del Regno <[email protected]>
Link: https://patchwork.kernel.org/project/dri-devel/patch/[email protected]/
Signed-off-by: Chun-Kuang Hu <[email protected]>

Author: AngeloGioacchino Del Regno

drivers/gpu/drm/mediatek/mtk_drm_drv.c

@@ -682,20 +682,29 @@ static int mtk_drm_bind(struct device *dev)
 	for (i = 0; i < private->data->mmsys_dev_num; i++)
 		private->all_drm_private[i]->drm = NULL;
 err_put_dev:
+	for (i = 0; i < private->data->mmsys_dev_num; i++) {
+		/* For device_find_child in mtk_drm_get_all_priv() */
+		put_device(private->all_drm_private[i]->dev);
+	}
 	put_device(private->mutex_dev);
 	return ret;
 }
 
 static void mtk_drm_unbind(struct device *dev)
 {
 	struct mtk_drm_private *private = dev_get_drvdata(dev);
+	int i;
 
 	/* for multi mmsys dev, unregister drm dev in mmsys master */
 	if (private->drm_master) {
 		drm_dev_unregister(private->drm);
 		mtk_drm_kms_deinit(private->drm);
 		drm_dev_put(private->drm);
 
+		for (i = 0; i < private->data->mmsys_dev_num; i++) {
+			/* For device_find_child in mtk_drm_get_all_priv() */
+			put_device(private->all_drm_private[i]->dev);
+		}
 		put_device(private->mutex_dev);
 	}
 	private->mtk_drm_bound = false;