From: Jyri Sarha <jsarha@ti.com>
Date: Thu, 26 Apr 2018 11:07:00 +0300
Subject: drm/panel: Add device_link from panel device to DRM device
Git-commit: 0c08754b59da5557532d946599854e6df28edc22
Patch-mainline: v4.19-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Add device_link from panel device (supplier) to DRM device (consumer)
when drm_panel_attach() is called. This patch should protect the master
DRM driver if an attached panel driver unbinds while it is in use. The
device_link should make sure the DRM device is unbound before the panel
driver becomes unavailable.

The device_link is removed when drm_panel_detach() is called. The
drm_panel_detach() should be called by the consumer DRM driver, not the
panel driver, otherwise both drivers are racing to delete the same link.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b53584fd988d045c13de22d81825395b0ae0aad7.1524727888.git.jsarha@ti.com

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/drm_panel.c |   10 ++++++++++
 include/drm/drm_panel.h     |    1 +
 2 files changed, 11 insertions(+)

--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -24,6 +24,7 @@
 #include <linux/err.h>
 #include <linux/module.h>
 
+#include <drm/drm_device.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_panel.h>
 
@@ -104,6 +105,13 @@ int drm_panel_attach(struct drm_panel *p
 	if (panel->connector)
 		return -EBUSY;
 
+	panel->link = device_link_add(connector->dev->dev, panel->dev, 0);
+	if (!panel->link) {
+		dev_err(panel->dev, "failed to link panel to %s\n",
+			dev_name(connector->dev->dev));
+		return -EINVAL;
+	}
+
 	panel->connector = connector;
 	panel->drm = connector->dev;
 
@@ -125,6 +133,8 @@ EXPORT_SYMBOL(drm_panel_attach);
  */
 int drm_panel_detach(struct drm_panel *panel)
 {
+	device_link_del(panel->link);
+
 	panel->connector = NULL;
 	panel->drm = NULL;
 
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -89,6 +89,7 @@ struct drm_panel {
 	struct drm_device *drm;
 	struct drm_connector *connector;
 	struct device *dev;
+	struct device_link *link;
 
 	const struct drm_panel_funcs *funcs;