Re: [PATCH v5 5/9] drm/imx: Add support for i.MX94 DCIF

Hi Luca,

On Fri, Oct 31, 2025 at 09:14:45AM +0100, Luca Ceresoli wrote:

Hello Laurentiu,

On Thu Sep 11, 2025 at 1:37 PM CEST, Laurentiu Palcu wrote:

...

quoted

+static struct drm_bridge *dcif_crtc_get_bridge(struct drm_crtc *crtc,
+					       struct drm_crtc_state *crtc_state)
+{
+	struct drm_connector_state *conn_state;
+	struct drm_encoder *encoder;
+	struct drm_connector *conn;
+	struct drm_bridge *bridge;
+	int i;
+
+	for_each_new_connector_in_state(crtc_state->state, conn, conn_state, i) {
+		if (crtc != conn_state->crtc)
+			continue;
+
+		encoder = conn_state->best_encoder;
+
+		bridge = drm_bridge_chain_get_first_bridge(encoder);

The bridge returned by drm_bridge_chain_get_first_bridge() is refcounted
since v6.18-rc1 [0], so you have to put that reference...

quoted

+		if (bridge)
+			return bridge;
+	}
+
+	return NULL;
+}
+
+static void dcif_crtc_query_output_bus_format(struct drm_crtc *crtc,
+					      struct drm_crtc_state *crtc_state)
+{
+	struct dcif_crtc_state *dcif_state = to_dcif_crtc_state(crtc_state);
+	struct drm_bridge_state *bridge_state;
+	struct drm_bridge *bridge;
+
+	dcif_state->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
+	dcif_state->bus_flags = 0;
+
+	bridge = dcif_crtc_get_bridge(crtc, crtc_state);
+	if (!bridge)
+		return;
+
+	bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state, bridge);
+	if (!bridge_state)
+		return;
+
+	dcif_state->bus_format = bridge_state->input_bus_cfg.format;
+	dcif_state->bus_flags = bridge_state->input_bus_cfg.flags;

...perhaps here, when both the bridge pointer and the bridge_state pointer
referencing it go out of scope.

quoted

+}

You can just call drm_bridge_put(bridge) there, or (at your option) use a
cleanup action:

 static void dcif_crtc_query_output_bus_format(struct drm_crtc *crtc,
                                               struct drm_crtc_state *crtc_state)
 {
         struct dcif_crtc_state *dcif_state = to_dcif_crtc_state(crtc_state);
         struct drm_bridge_state *bridge_state;
-        struct drm_bridge *bridge;

         dcif_state->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
         dcif_state->bus_flags = 0;

-        bridge = dcif_crtc_get_bridge(crtc, crtc_state);
+        struct drm_bridge *bridge __free(drm_bridge_put) = dcif_crtc_get_bridge(crtc, crtc_state);
         if (!bridge)
                 return;

         bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state, bridge);
         if (!bridge_state)
                 return;

         dcif_state->bus_format = bridge_state->input_bus_cfg.format;
         dcif_state->bus_flags = bridge_state->input_bus_cfg.flags;
 }

This would call drm_bridge_put() at end of scope, i.e. end of function.

You can also have a look at recent commits involving drm_bridge_put (git
log -p -Gdrm_bridge_put v6.16..origin/master) to see how other parts of the
kernel have added drm_bridge_put().

Thanks for reviewing and the heads-up on using drm_bridge_put(). I'll
send a v6 next week with the fix.

Thanks,
Laurentiu

[0] https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/8fa5909400f377351836419223c33f1131f0f7d3

Best regards,
Luca

---
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com