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

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Message-Id: <DDWCVYBQSV10.2MFZFEEHPYJY4@bootlin.com>
Date: Fri, 31 Oct 2025 09:14:45 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Laurentiu Palcu" <laurentiu.palcu@....nxp.com>, <imx@...ts.linux.dev>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard"
 <mripard@...nel.org>, "Thomas Zimmermann" <tzimmermann@...e.de>, "David
 Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Shawn Guo"
 <shawnguo@...nel.org>, "Sascha Hauer" <s.hauer@...gutronix.de>,
 "Pengutronix Kernel Team" <kernel@...gutronix.de>, "Fabio Estevam"
 <festevam@...il.com>
Cc: <dri-devel@...ts.freedesktop.org>, "Sandor Yu" <sandor.yu@....com>,
 <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 5/9] drm/imx: Add support for i.MX94 DCIF

Hello Laurentiu,

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

...

> +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...

> +		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.

> +}

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().

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

Best regards,
Luca

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