staging: drm/imx: fix pageflip events during device close

During a device close the drm core frees all pending events in
drm_events_release(). If at that time a pageflip is pending the
interrupt handler will try to complete the now unitialized
event resulting in a NULL pointer exception. Seen on imx-drm
when userspace is killed during a page flip.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/imx-drm/imx-drm-core.c

@@ -185,6 +185,18 @@ static void imx_drm_disable_vblank(struct drm_device *drm, int crtc)
 	imx_drm_crtc->imx_drm_helper_funcs.disable_vblank(imx_drm_crtc->crtc);
 }
 
+static void imx_drm_driver_preclose(struct drm_device *drm,
+		struct drm_file *file)
+{
+	int i;
+
+	if (!file->is_master)
+		return;
+
+	for (i = 0; i < 4; i++)
+		imx_drm_disable_vblank(drm , i);
+}
+
 static const struct file_operations imx_drm_driver_fops = {
 	.owner = THIS_MODULE,
 	.open = drm_open,
@@ -766,6 +778,7 @@ static struct drm_driver imx_drm_driver = {
 	.load			= imx_drm_driver_load,
 	.unload			= imx_drm_driver_unload,
 	.lastclose		= imx_drm_driver_lastclose,
+	.preclose		= imx_drm_driver_preclose,
 	.gem_free_object	= drm_gem_cma_free_object,
 	.gem_vm_ops		= &drm_gem_cma_vm_ops,
 	.dumb_create		= drm_gem_cma_dumb_create,

drivers/staging/imx-drm/ipuv3-crtc.c

@@ -368,10 +368,6 @@ static struct drm_crtc_helper_funcs ipu_helper_funcs = {
 
 static int ipu_enable_vblank(struct drm_crtc *crtc)
 {
-	struct ipu_crtc *ipu_crtc = to_ipu_crtc(crtc);
-
-	enable_irq(ipu_crtc->irq);
-
 	return 0;
 }
 
@@ -379,7 +375,8 @@ static void ipu_disable_vblank(struct drm_crtc *crtc)
 {
 	struct ipu_crtc *ipu_crtc = to_ipu_crtc(crtc);
 
-	disable_irq(ipu_crtc->irq);
+	ipu_crtc->page_flip_event = NULL;
+	ipu_crtc->newfb = NULL;
 }
 
 static int ipu_set_interface_pix_fmt(struct drm_crtc *crtc, u32 encoder_type,
@@ -502,8 +499,6 @@ static int ipu_crtc_init(struct ipu_crtc *ipu_crtc,
 		goto err_put_resources;
 	}
 
-	disable_irq(ipu_crtc->irq);
-
 	return 0;
 
 err_put_resources: