[PATCH] drm/bridge: panel: Check device dependency before managing device link

[Liu Ying]

Some panel devices already depend on DRM device, like the panel in
arch/arm/boot/dts/st/ste-ux500-samsung-skomer.dts, because DRM device is
the ancestor of those panel devices.  device_link_add() would fail by
returning a NULL pointer for those panel devices because of the existing
dependency.  So, check the dependency by calling device_is_dependent()
before adding or deleting device link between panel device and DRM device
so that the link is managed only for independent panel devices.

Fixes: 887878014534 ("drm/bridge: panel: Fix device link for 
DRM_BRIDGE_ATTACH_NO_CONNECTOR")
Fixes: 199cf07ebd2b ("drm/bridge: panel: Add a device link between drm device 
and panel device")
Reported-by: Linus Walleij <linus.wall...@linaro.org>
Closes: 
https://lore.kernel.org/lkml/cacrpkdagzxd6hbix7mvunjajtmepg00pp6+nj1p0jrfj-ar...@mail.gmail.com/T/
Tested-by: Linus Walleij <linus.wall...@linaro.org>
Signed-off-by: Liu Ying <victor....@nxp.com>
---
 drivers/gpu/drm/bridge/panel.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index e48823a4f1ed..5e8980023407 100644
--- a/drivers/gpu/drm/bridge/panel.c
+++ b/drivers/gpu/drm/bridge/panel.c
@@ -23,6 +23,7 @@ struct panel_bridge {
        struct drm_panel *panel;
        struct device_link *link;
        u32 connector_type;
+       bool is_independent;
 };
 
 static inline struct panel_bridge *
@@ -67,12 +68,17 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
        struct drm_device *drm_dev = bridge->dev;
        int ret;
 
-       panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
-                                            DL_FLAG_STATELESS);
-       if (!panel_bridge->link) {
-               DRM_ERROR("Failed to add device link between %s and %s\n",
-                         dev_name(drm_dev->dev), dev_name(panel->dev));
-               return -EINVAL;
+       panel_bridge->is_independent = !device_is_dependent(drm_dev->dev,
+                                                           panel->dev);
+
+       if (panel_bridge->is_independent) {
+               panel_bridge->link = device_link_add(drm_dev->dev, panel->dev,
+                                                    DL_FLAG_STATELESS);
+               if (!panel_bridge->link) {
+                       DRM_ERROR("Failed to add device link between %s and 
%s\n",
+                                 dev_name(drm_dev->dev), dev_name(panel->dev));
+                       return -EINVAL;
+               }
        }
 
        if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
@@ -80,7 +86,8 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
 
        if (!bridge->encoder) {
                DRM_ERROR("Missing encoder\n");
-               device_link_del(panel_bridge->link);
+               if (panel_bridge->is_independent)
+                       device_link_del(panel_bridge->link);
                return -ENODEV;
        }
 
@@ -92,7 +99,8 @@ static int panel_bridge_attach(struct drm_bridge *bridge,
                                 panel_bridge->connector_type);
        if (ret) {
                DRM_ERROR("Failed to initialize connector\n");
-               device_link_del(panel_bridge->link);
+               if (panel_bridge->is_independent)
+                       device_link_del(panel_bridge->link);
                return ret;
        }
 
@@ -115,7 +123,8 @@ static void panel_bridge_detach(struct drm_bridge *bridge)
        struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
        struct drm_connector *connector = &panel_bridge->connector;
 
-       device_link_del(panel_bridge->link);
+       if (panel_bridge->is_independent)
+               device_link_del(panel_bridge->link);
 
        /*
         * Cleanup the connector if we know it was initialized.
-- 
2.37.1