[PATCH v4] drm/bridge: imx8qxp-pxl2dpi: avoid ERR_PTR with device_node cleanup

[Guangshuo Li]

imx8qxp_pxl2dpi_get_available_ep_from_port() returns ERR_PTR()
on errors. imx8qxp_pxl2dpi_find_next_bridge() stores its return
value in a __free(device_node) variable before checking IS_ERR().
When the function returns on the error path, the cleanup action calls
of_node_put() on the ERR_PTR() value.

Do not let a device_node cleanup variable hold error pointers. Return
the error code from imx8qxp_pxl2dpi_get_available_ep_from_port()
directly and pass the endpoint node through an output argument. This
keeps the cleanup action operating only on NULL or a valid device_node,
while preserving the existing error codes.

Fixes: ceea3f7806a10 ("drm/bridge: imx8qxp-pxl2dpi: simplify put of device_node pointers")
Cc: stable at vger.kernel.org
Reviewed-by: Frank Li <Frank.Li at nxp.com>
Signed-off-by: Guangshuo Li <lgs201920130244 at gmail.com>
---
v4:
  - Drop the sentence mentioning the custom static analysis tool.
  - Add Frank's Reviewed-by tag.
  - No functional code changes.

v3:
  - Do not change DEFINE_FREE(device_node, ...).
  - Fix the driver pattern by making
    imx8qxp_pxl2dpi_get_available_ep_from_port() return an int and
    pass the endpoint via an output argument.
  - Update both callers so __free(device_node) never holds ERR_PTR().

v2:
  - Fix DEFINE_FREE(device_node, ...) directly.

 drivers/gpu/drm/bridge/imx/imx8qxp-pxl2dpi.c | 54 ++++++++++----------
 1 file changed, 26 insertions(+), 28 deletions(-)

diff --git a/drivers/gpu/drm/bridge/imx/imx8qxp-pxl2dpi.c b/drivers/gpu/drm/bridge/imx/imx8qxp-pxl2dpi.c
index 441fd32dc91c..881ebb811eb3 100644
--- a/drivers/gpu/drm/bridge/imx/imx8qxp-pxl2dpi.c
+++ b/drivers/gpu/drm/bridge/imx/imx8qxp-pxl2dpi.c
@@ -222,52 +222,52 @@ static const struct drm_bridge_funcs imx8qxp_pxl2dpi_bridge_funcs = {
 			imx8qxp_pxl2dpi_bridge_atomic_get_output_bus_fmts,
 };
 
-static struct device_node *
+static int
 imx8qxp_pxl2dpi_get_available_ep_from_port(struct imx8qxp_pxl2dpi *p2d,
-					   u32 port_id)
+					   u32 port_id,
+					   struct device_node **ep)
 {
-	struct device_node *port, *ep;
+	struct device_node *port __free(device_node) =
+		of_graph_get_port_by_id(p2d->dev->of_node, port_id);
 	int ep_cnt;
 
-	port = of_graph_get_port_by_id(p2d->dev->of_node, port_id);
+	*ep = NULL;
 	if (!port) {
 		DRM_DEV_ERROR(p2d->dev, "failed to get port@%u\n", port_id);
-		return ERR_PTR(-ENODEV);
+		return -ENODEV;
 	}
 
 	ep_cnt = of_get_available_child_count(port);
 	if (ep_cnt == 0) {
 		DRM_DEV_ERROR(p2d->dev, "no available endpoints of port@%u\n",
 			      port_id);
-		ep = ERR_PTR(-ENODEV);
-		goto out;
+		return -ENODEV;
 	} else if (ep_cnt > 1) {
 		DRM_DEV_ERROR(p2d->dev,
 			      "invalid available endpoints of port@%u\n",
 			      port_id);
-		ep = ERR_PTR(-EINVAL);
-		goto out;
+		return -EINVAL;
 	}
 
-	ep = of_get_next_available_child(port, NULL);
-	if (!ep) {
+	*ep = of_get_next_available_child(port, NULL);
+	if (!*ep) {
 		DRM_DEV_ERROR(p2d->dev,
 			      "failed to get available endpoint of port@%u\n",
 			      port_id);
-		ep = ERR_PTR(-ENODEV);
-		goto out;
+		return -ENODEV;
 	}
-out:
-	of_node_put(port);
-	return ep;
+
+	return 0;
 }
 
 static int imx8qxp_pxl2dpi_find_next_bridge(struct imx8qxp_pxl2dpi *p2d)
 {
-	struct device_node *ep __free(device_node) =
-		imx8qxp_pxl2dpi_get_available_ep_from_port(p2d, 1);
-	if (IS_ERR(ep))
-		return PTR_ERR(ep);
+	struct device_node *ep __free(device_node) = NULL;
+	int ret;
+
+	ret = imx8qxp_pxl2dpi_get_available_ep_from_port(p2d, 1, &ep);
+	if (ret)
+		return ret;
 
 	struct device_node *remote __free(device_node) = of_graph_get_remote_port_parent(ep);
 	if (!remote || !of_device_is_available(remote)) {
@@ -287,26 +287,24 @@ static int imx8qxp_pxl2dpi_find_next_bridge(struct imx8qxp_pxl2dpi *p2d)
 
 static int imx8qxp_pxl2dpi_set_pixel_link_sel(struct imx8qxp_pxl2dpi *p2d)
 {
-	struct device_node *ep;
+	struct device_node *ep __free(device_node) = NULL;
 	struct of_endpoint endpoint;
 	int ret;
 
-	ep = imx8qxp_pxl2dpi_get_available_ep_from_port(p2d, 0);
-	if (IS_ERR(ep))
-		return PTR_ERR(ep);
+	ret = imx8qxp_pxl2dpi_get_available_ep_from_port(p2d, 0, &ep);
+	if (ret)
+		return ret;
 
 	ret = of_graph_parse_endpoint(ep, &endpoint);
 	if (ret) {
 		DRM_DEV_ERROR(p2d->dev,
 			      "failed to parse endpoint of port at 0: %d\n", ret);
-		goto out;
+		return ret;
 	}
 
 	p2d->pl_sel = endpoint.id;
-out:
-	of_node_put(ep);
 
-	return ret;
+	return 0;
 }
 
 static int imx8qxp_pxl2dpi_parse_dt_companion(struct imx8qxp_pxl2dpi *p2d)
-- 
2.43.0