media: imx: Unregister csc/scaler only if registered

The csc/scaler device pointer (imxmd->m2m_vdev) is assigned
after the imx media device v4l2-async probe completes,
therefore we need to check if the device is non-NULL
before trying to unregister it.

This can be the case if the non-completed imx media device
is unbinded (or the driver is removed), leading to a kernel oops.

Fixes: a8ef0488 ("media: imx: add csc/scaler mem2mem device")
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/staging/media/imx/imx-media-dev.c

@@ -53,6 +53,7 @@ static int imx6_media_probe_complete(struct v4l2_async_notifier *notifier)
 	imxmd->m2m_vdev = imx_media_csc_scaler_device_init(imxmd);
 	if (IS_ERR(imxmd->m2m_vdev)) {
 		ret = PTR_ERR(imxmd->m2m_vdev);
+		imxmd->m2m_vdev = NULL;
 		goto unlock;
 	}
 
@@ -107,10 +108,14 @@ static int imx_media_remove(struct platform_device *pdev)
 
 	v4l2_info(&imxmd->v4l2_dev, "Removing imx-media\n");
 
+	if (imxmd->m2m_vdev) {
+		imx_media_csc_scaler_device_unregister(imxmd->m2m_vdev);
+		imxmd->m2m_vdev = NULL;
+	}
+
 	v4l2_async_notifier_unregister(&imxmd->notifier);
 	imx_media_unregister_ipu_internal_subdevs(imxmd);
 	v4l2_async_notifier_cleanup(&imxmd->notifier);
-	imx_media_csc_scaler_device_unregister(imxmd->m2m_vdev);
 	media_device_unregister(&imxmd->md);
 	v4l2_device_unregister(&imxmd->v4l2_dev);
 	media_device_cleanup(&imxmd->md);