drm/bridge: Extend bridge API to disable connector creation

Most bridge drivers create a DRM connector to model the connector at the
output of the bridge. This model is historical and has worked pretty
well so far, but causes several issues:

- It prevents supporting more complex display pipelines where DRM
connector operations are split over multiple components. For instance a
pipeline with a bridge connected to the DDC signals to read EDID data,
and another one connected to the HPD signal to detect connection and
disconnection, will not be possible to support through this model.

- It requires every bridge driver to implement similar connector
handling code, resulting in code duplication.

- It assumes that a bridge will either be wired to a connector or to
another bridge, but doesn't support bridges that can be used in both
positions very well (although there is some ad-hoc support for this in
the analogix_dp bridge driver).

In order to solve these issues, ownership of the connector should be
moved to the display controller driver (where it can be implemented
using helpers provided by the core).

Extend the bridge API to allow disabling connector creation in bridge
drivers as a first step towards the new model. The new flags argument to
the bridge .attach() operation allows instructing the bridge driver to
skip creating a connector. Unconditionally set the new flags argument to
0 for now to keep the existing behaviour, and modify all existing bridge
drivers to return an error when connector creation is not requested as
they don't support this feature yet.

The change is based on the following semantic patch, with manual review
and edits.

@ rule1 @
identifier funcs;
identifier fn;
@@
struct drm_bridge_funcs funcs = {
...,
.attach = fn
};

@ depends on rule1 @
identifier rule1.fn;
identifier bridge;
statement S, S1;
@@
int fn(
struct drm_bridge *bridge
+ , enum drm_bridge_attach_flags flags
)
{
... when != S
+ if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+ DRM_ERROR("Fix bridge driver to make connector optional!");
+ return -EINVAL;
+ }
+
S1
...
}

@ depends on rule1 @
identifier rule1.fn;
identifier bridge, flags;
expression E1, E2, E3;
@@
int fn(
struct drm_bridge *bridge,
enum drm_bridge_attach_flags flags
) {
<...
drm_bridge_attach(E1, E2, E3
+ , flags
)
...>
}

@@
expression E1, E2, E3;
@@
drm_bridge_attach(E1, E2, E3
+ , 0
)

Signed-off-by: Laurent Pinchart <[e-mail]>
Reviewed-by: Boris Brezillon <[e-mail]>
Acked-by: Sam Ravnborg <[e-mail]>
Reviewed-by: Tomi Valkeinen <[e-mail]>
Tested-by: Sebastian Reichel <[e-mail]>
Reviewed-by: Sebastian Reichel <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/arc/arcpgu_hdmi.c

···
 		return ret;
 
 	/* Link drm_bridge to encoder */
-	ret = drm_bridge_attach(encoder, bridge, NULL);
+	ret = drm_bridge_attach(encoder, bridge, NULL, 0);
 	if (ret)
 		drm_encoder_cleanup(encoder);
 

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_output.c

···
 	}
 
 	if (bridge) {
-		ret = drm_bridge_attach(&output->encoder, bridge, NULL);
+		ret = drm_bridge_attach(&output->encoder, bridge, NULL, 0);
 		if (!ret)
 			return 0;
 

drivers/gpu/drm/bridge/adv7511/adv7511_drv.c

···
 	adv7511_mode_set(adv, mode, adj_mode);
 }
 
-static int adv7511_bridge_attach(struct drm_bridge *bridge)
+static int adv7511_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct adv7511 *adv = bridge_to_adv7511(bridge);
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");

drivers/gpu/drm/bridge/analogix/analogix-anx6345.c

···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int anx6345_bridge_attach(struct drm_bridge *bridge)
+static int anx6345_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct anx6345 *anx6345 = bridge_to_anx6345(bridge);
 	int err;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");

drivers/gpu/drm/bridge/analogix/analogix-anx78xx.c

···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int anx78xx_bridge_attach(struct drm_bridge *bridge)
+static int anx78xx_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct anx78xx *anx78xx = bridge_to_anx78xx(bridge);
 	int err;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");

drivers/gpu/drm/bridge/analogix/analogix_dp_core.c

···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int analogix_dp_bridge_attach(struct drm_bridge *bridge)
+static int analogix_dp_bridge_attach(struct drm_bridge *bridge,
+				     enum drm_bridge_attach_flags flags)
 {
 	struct analogix_dp_device *dp = bridge->driver_private;
 	struct drm_encoder *encoder = dp->encoder;
 	struct drm_connector *connector = NULL;
 	int ret = 0;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");
···
 	bridge->driver_private = dp;
 	bridge->funcs = &analogix_dp_bridge_funcs;
 
-	ret = drm_bridge_attach(dp->encoder, bridge, NULL);
+	ret = drm_bridge_attach(dp->encoder, bridge, NULL, 0);
 	if (ret) {
 		DRM_ERROR("failed to attach drm bridge\n");
 		return -EINVAL;

drivers/gpu/drm/bridge/cdns-dsi.c

···
 	return 0;
 }
 
-static int cdns_dsi_bridge_attach(struct drm_bridge *bridge)
+static int cdns_dsi_bridge_attach(struct drm_bridge *bridge,
+				  enum drm_bridge_attach_flags flags)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
···
 		return -ENOTSUPP;
 	}
 
-	return drm_bridge_attach(bridge->encoder, output->bridge, bridge);
+	return drm_bridge_attach(bridge->encoder, output->bridge, bridge,
+				 flags);
 }
 
 static enum drm_mode_status

drivers/gpu/drm/bridge/dumb-vga-dac.c

···
 	.atomic_destroy_state	= drm_atomic_helper_connector_destroy_state,
 };
 
-static int dumb_vga_attach(struct drm_bridge *bridge)
+static int dumb_vga_attach(struct drm_bridge *bridge,
+			   enum drm_bridge_attach_flags flags)
 {
 	struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Missing encoder\n");

drivers/gpu/drm/bridge/lvds-codec.c

···
 	return container_of(bridge, struct lvds_codec, bridge);
 }
 
-static int lvds_codec_attach(struct drm_bridge *bridge)
+static int lvds_codec_attach(struct drm_bridge *bridge,
+			     enum drm_bridge_attach_flags flags)
 {
 	struct lvds_codec *lvds_codec = to_lvds_codec(bridge);
 
 	return drm_bridge_attach(bridge->encoder, lvds_codec->panel_bridge,
-				 bridge);
+				 bridge, flags);
 }
 
 static void lvds_codec_enable(struct drm_bridge *bridge)

drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c

···
 	return IRQ_HANDLED;
 }
 
-static int ge_b850v3_lvds_attach(struct drm_bridge *bridge)
+static int ge_b850v3_lvds_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct drm_connector *connector = &ge_b850v3_lvds_ptr->connector;
 	struct i2c_client *stdp4028_i2c
 			= ge_b850v3_lvds_ptr->stdp4028_i2c;
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");

drivers/gpu/drm/bridge/nxp-ptn3460.c

···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int ptn3460_bridge_attach(struct drm_bridge *bridge)
+static int ptn3460_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct ptn3460_bridge *ptn_bridge = bridge_to_ptn3460(bridge);
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");

drivers/gpu/drm/bridge/panel.c

···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int panel_bridge_attach(struct drm_bridge *bridge)
+static int panel_bridge_attach(struct drm_bridge *bridge,
+			       enum drm_bridge_attach_flags flags)
 {
 	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
 	struct drm_connector *connector = &panel_bridge->connector;
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Missing encoder\n");

drivers/gpu/drm/bridge/parade-ps8622.c

···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int ps8622_attach(struct drm_bridge *bridge)
+static int ps8622_attach(struct drm_bridge *bridge,
+			 enum drm_bridge_attach_flags flags)
 {
 	struct ps8622_bridge *ps8622 = bridge_to_ps8622(bridge);
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		DRM_ERROR("Parent encoder object not found");

drivers/gpu/drm/bridge/parade-ps8640.c

···
 		DRM_ERROR("cannot disable regulators %d\n", ret);
 }
 
-static int ps8640_bridge_attach(struct drm_bridge *bridge)
+static int ps8640_bridge_attach(struct drm_bridge *bridge,
+				enum drm_bridge_attach_flags flags)
 {
 	struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
 	struct device *dev = &ps_bridge->page[0]->dev;
···
 
 	/* Attach the panel-bridge to the dsi bridge */
 	return drm_bridge_attach(bridge->encoder, ps_bridge->panel_bridge,
-				 &ps_bridge->bridge);
+				 &ps_bridge->bridge, flags);
 
 err_dsi_attach:
 	mipi_dsi_device_unregister(dsi);

drivers/gpu/drm/bridge/sii902x.c

···
 	mutex_unlock(&sii902x->mutex);
 }
 
-static int sii902x_bridge_attach(struct drm_bridge *bridge)
+static int sii902x_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct sii902x *sii902x = bridge_to_sii902x(bridge);
 	struct drm_device *drm = bridge->dev;
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	drm_connector_helper_add(&sii902x->connector,
 				 &sii902x_connector_helper_funcs);

drivers/gpu/drm/bridge/sil-sii8620.c

···
 	return container_of(bridge, struct sii8620, bridge);
 }
 
-static int sii8620_attach(struct drm_bridge *bridge)
+static int sii8620_attach(struct drm_bridge *bridge,
+			  enum drm_bridge_attach_flags flags)
 {
 	struct sii8620 *ctx = bridge_to_sii8620(bridge);
 

drivers/gpu/drm/bridge/synopsys/dw-hdmi.c

···
 	.atomic_check = dw_hdmi_connector_atomic_check,
 };
 
-static int dw_hdmi_bridge_attach(struct drm_bridge *bridge)
+static int dw_hdmi_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct dw_hdmi *hdmi = bridge->driver_private;
 	struct drm_encoder *encoder = bridge->encoder;
 	struct drm_connector *connector = &hdmi->connector;
 	struct cec_connector_info conn_info;
 	struct cec_notifier *notifier;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	connector->interlace_allowed = 1;
 	connector->polled = DRM_CONNECTOR_POLL_HPD;
···
 	if (IS_ERR(hdmi))
 		return hdmi;
 
-	ret = drm_bridge_attach(encoder, &hdmi->bridge, NULL);
+	ret = drm_bridge_attach(encoder, &hdmi->bridge, NULL, 0);
 	if (ret) {
 		dw_hdmi_remove(hdmi);
 		DRM_ERROR("Failed to initialize bridge with drm\n");

drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c

···
 	return mode_status;
 }
 
-static int dw_mipi_dsi_bridge_attach(struct drm_bridge *bridge)
+static int dw_mipi_dsi_bridge_attach(struct drm_bridge *bridge,
+				     enum drm_bridge_attach_flags flags)
 {
 	struct dw_mipi_dsi *dsi = bridge_to_dsi(bridge);
 
···
 	bridge->encoder->encoder_type = DRM_MODE_ENCODER_DSI;
 
 	/* Attach the panel-bridge to the dsi bridge */
-	return drm_bridge_attach(bridge->encoder, dsi->panel_bridge, bridge);
+	return drm_bridge_attach(bridge->encoder, dsi->panel_bridge, bridge,
+				 flags);
 }
 
 static const struct drm_bridge_funcs dw_mipi_dsi_bridge_funcs = {
···
 {
 	int ret;
 
-	ret = drm_bridge_attach(encoder, &dsi->bridge, NULL);
+	ret = drm_bridge_attach(encoder, &dsi->bridge, NULL, 0);
 	if (ret) {
 		DRM_ERROR("Failed to initialize bridge with drm\n");
 		return ret;

drivers/gpu/drm/bridge/tc358764.c

···
 		dev_err(ctx->dev, "error enabling panel (%d)\n", ret);
 }
 
-static int tc358764_attach(struct drm_bridge *bridge)
+static int tc358764_attach(struct drm_bridge *bridge,
+			   enum drm_bridge_attach_flags flags)
 {
 	struct tc358764 *ctx = bridge_to_tc358764(bridge);
 	struct drm_device *drm = bridge->dev;
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	ctx->connector.polled = DRM_CONNECTOR_POLL_HPD;
 	ret = drm_connector_init(drm, &ctx->connector,

drivers/gpu/drm/bridge/tc358767.c

···
 #include <drm/drm_edid.h>
 #include <drm/drm_of.h>
 #include <drm/drm_panel.h>
+#include <drm/drm_print.h>
 #include <drm/drm_probe_helper.h>
 
 /* Registers */
···
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
-static int tc_bridge_attach(struct drm_bridge *bridge)
+static int tc_bridge_attach(struct drm_bridge *bridge,
+			    enum drm_bridge_attach_flags flags)
 {
 	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
 	struct tc_data *tc = bridge_to_tc(bridge);
 	struct drm_device *drm = bridge->dev;
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	/* Create DP/eDP connector */
 	drm_connector_helper_add(&tc->connector, &tc_connector_helper_funcs);

drivers/gpu/drm/bridge/tc358768.c

···
 	.transfer = tc358768_dsi_host_transfer,
 };
 
-static int tc358768_bridge_attach(struct drm_bridge *bridge)
+static int tc358768_bridge_attach(struct drm_bridge *bridge,
+				  enum drm_bridge_attach_flags flags)
 {
 	struct tc358768_priv *priv = bridge_to_tc358768(bridge);
 
···
 		return -ENOTSUPP;
 	}
 
-	return drm_bridge_attach(bridge->encoder, priv->output.bridge, bridge);
+	return drm_bridge_attach(bridge->encoder, priv->output.bridge, bridge,
+				 flags);
 }
 
 static enum drm_mode_status

drivers/gpu/drm/bridge/thc63lvd1024.c

···
 	return container_of(bridge, struct thc63_dev, bridge);
 }
 
-static int thc63_attach(struct drm_bridge *bridge)
+static int thc63_attach(struct drm_bridge *bridge,
+			enum drm_bridge_attach_flags flags)
 {
 	struct thc63_dev *thc63 = to_thc63(bridge);
 
-	return drm_bridge_attach(bridge->encoder, thc63->next, bridge);
+	return drm_bridge_attach(bridge->encoder, thc63->next, bridge, flags);
 }
 
 static enum drm_mode_status thc63_mode_valid(struct drm_bridge *bridge,

drivers/gpu/drm/bridge/ti-sn65dsi86.c

···
 				       pdata->supplies);
 }
 
-static int ti_sn_bridge_attach(struct drm_bridge *bridge)
+static int ti_sn_bridge_attach(struct drm_bridge *bridge,
+			       enum drm_bridge_attach_flags flags)
 {
 	int ret, val;
 	struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge);
···
 						   .channel = 0,
 						   .node = NULL,
 						 };
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	ret = drm_connector_init(bridge->dev, &pdata->connector,
 				 &ti_sn_bridge_connector_funcs,

drivers/gpu/drm/bridge/ti-tfp410.c

···
 	.atomic_destroy_state	= drm_atomic_helper_connector_destroy_state,
 };
 
-static int tfp410_attach(struct drm_bridge *bridge)
+static int tfp410_attach(struct drm_bridge *bridge,
+			 enum drm_bridge_attach_flags flags)
 {
 	struct tfp410 *dvi = drm_bridge_to_tfp410(bridge);
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	if (!bridge->encoder) {
 		dev_err(dvi->dev, "Missing encoder\n");

drivers/gpu/drm/drm_bridge.c

···
  * @encoder: DRM encoder
  * @bridge: bridge to attach
  * @previous: previous bridge in the chain (optional)
+ * @flags: DRM_BRIDGE_ATTACH_* flags
  *
  * Called by a kms driver to link the bridge to an encoder's chain. The previous
  * argument specifies the previous bridge in the chain. If NULL, the bridge is
···
  * Zero on success, error code on failure
  */
 int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
-		      struct drm_bridge *previous)
+		      struct drm_bridge *previous,
+		      enum drm_bridge_attach_flags flags)
 {
 	int ret;
 
···
 		list_add(&bridge->chain_node, &encoder->bridge_chain);
 
 	if (bridge->funcs->attach) {
-		ret = bridge->funcs->attach(bridge);
+		ret = bridge->funcs->attach(bridge, flags);
 		if (ret < 0)
 			goto err_reset_bridge;
 	}
···
  *   allows providing a single static const &drm_bridge_funcs instance in
  *   bridge drivers, improving security by storing function pointers in
  *   read-only memory.
+ *
+ *   In order to ease transition, bridge drivers may support both the old and
+ *   new models by making connector creation optional and implementing the
+ *   connected-related bridge operations. Connector creation is then controlled
+ *   by the flags argument to the drm_bridge_attach() function. Display drivers
+ *   that support the new model and create connectors themselves shall set the
+ *   %DRM_BRIDGE_ATTACH_NO_CONNECTOR flag, and bridge drivers shall then skip
+ *   connector creation. For intermediate bridges in the chain, the flag shall
+ *   be passed to the drm_bridge_attach() call for the downstream bridge.
+ *   Bridge drivers that implement the new model only shall return an error
+ *   from their &drm_bridge_funcs.attach handler when the
+ *   %DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is not set. New display drivers
+ *   should use the new model, and convert the bridge drivers they use if
+ *   needed, in order to gradually transition to the new model.
  */
 
 /**

drivers/gpu/drm/drm_simple_kms_helper.c

···
 int drm_simple_display_pipe_attach_bridge(struct drm_simple_display_pipe *pipe,
 					  struct drm_bridge *bridge)
 {
-	return drm_bridge_attach(&pipe->encoder, bridge, NULL);
+	return drm_bridge_attach(&pipe->encoder, bridge, NULL, 0);
 }
 EXPORT_SYMBOL(drm_simple_display_pipe_attach_bridge);
 

drivers/gpu/drm/exynos/exynos_dp.c

···
 
 	/* Pre-empt DP connector creation if there's a bridge */
 	if (dp->ptn_bridge) {
-		ret = drm_bridge_attach(&dp->encoder, dp->ptn_bridge, bridge);
+		ret = drm_bridge_attach(&dp->encoder, dp->ptn_bridge, bridge,
+					0);
 		if (ret) {
 			DRM_DEV_ERROR(dp->dev,
 				      "Failed to attach bridge to drm\n");

drivers/gpu/drm/exynos/exynos_drm_dsi.c

···
 
 	out_bridge  = of_drm_find_bridge(device->dev.of_node);
 	if (out_bridge) {
-		drm_bridge_attach(encoder, out_bridge, NULL);
+		drm_bridge_attach(encoder, out_bridge, NULL, 0);
 		dsi->out_bridge = out_bridge;
 		list_splice_init(&encoder->bridge_chain, &dsi->bridge_chain);
 	} else {
···
 	if (dsi->in_bridge_node) {
 		in_bridge = of_drm_find_bridge(dsi->in_bridge_node);
 		if (in_bridge)
-			drm_bridge_attach(encoder, in_bridge, NULL);
+			drm_bridge_attach(encoder, in_bridge, NULL, 0);
 	}
 
 	return mipi_dsi_host_register(&dsi->dsi_host);

drivers/gpu/drm/exynos/exynos_hdmi.c

···
 	drm_connector_attach_encoder(connector, encoder);
 
 	if (hdata->bridge) {
-		ret = drm_bridge_attach(encoder, hdata->bridge, NULL);
+		ret = drm_bridge_attach(encoder, hdata->bridge, NULL, 0);
 		if (ret)
 			DRM_DEV_ERROR(hdata->dev, "Failed to attach bridge\n");
 	}

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c

···
 		return fsl_dcu_attach_panel(fsl_dev, panel);
 	}
 
-	return drm_bridge_attach(&fsl_dev->encoder, bridge, NULL);
+	return drm_bridge_attach(&fsl_dev->encoder, bridge, NULL, 0);
 }

drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c

···
 	int ret;
 
 	/* associate the bridge to dsi encoder */
-	ret = drm_bridge_attach(encoder, bridge, NULL);
+	ret = drm_bridge_attach(encoder, bridge, NULL, 0);
 	if (ret) {
 		DRM_ERROR("failed to attach external bridge\n");
 		return ret;

drivers/gpu/drm/i2c/tda998x_drv.c

···
 
 /* DRM bridge functions */
 
-static int tda998x_bridge_attach(struct drm_bridge *bridge)
+static int tda998x_bridge_attach(struct drm_bridge *bridge,
+				 enum drm_bridge_attach_flags flags)
 {
 	struct tda998x_priv *priv = bridge_to_tda998x_priv(bridge);
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	return tda998x_connector_init(priv, bridge->dev);
 }
···
 	if (ret)
 		goto err_encoder;
 
-	ret = drm_bridge_attach(&priv->encoder, &priv->bridge, NULL);
+	ret = drm_bridge_attach(&priv->encoder, &priv->bridge, NULL, 0);
 	if (ret)
 		goto err_bridge;
 

drivers/gpu/drm/imx/imx-ldb.c

···
 
 	if (imx_ldb_ch->bridge) {
 		ret = drm_bridge_attach(&imx_ldb_ch->encoder,
-					imx_ldb_ch->bridge, NULL);
+					imx_ldb_ch->bridge, NULL, 0);
 		if (ret) {
 			DRM_ERROR("Failed to initialize bridge with drm\n");
 			return ret;

drivers/gpu/drm/imx/parallel-display.c

···
 			 DRM_MODE_ENCODER_NONE, NULL);
 
 	imxpd->bridge.funcs = &imx_pd_bridge_funcs;
-	drm_bridge_attach(encoder, &imxpd->bridge, NULL);
+	drm_bridge_attach(encoder, &imxpd->bridge, NULL, 0);
 
 	if (!imxpd->next_bridge) {
 		drm_connector_helper_add(&imxpd->connector,
···
 
 	if (imxpd->next_bridge) {
 		ret = drm_bridge_attach(encoder, imxpd->next_bridge,
-					&imxpd->bridge);
+					&imxpd->bridge, 0);
 		if (ret < 0) {
 			dev_err(imxpd->dev, "failed to attach bridge: %d\n",
 				ret);

drivers/gpu/drm/ingenic/ingenic-drm.c

···
 		return ret;
 	}
 
-	ret = drm_bridge_attach(&priv->encoder, bridge, NULL);
+	ret = drm_bridge_attach(&priv->encoder, bridge, NULL, 0);
 	if (ret) {
 		dev_err(dev, "Unable to attach bridge");
 		return ret;

drivers/gpu/drm/mcde/mcde_dsi.c

···
 	clk_disable_unprepare(d->lp_clk);
 }
 
-static int mcde_dsi_bridge_attach(struct drm_bridge *bridge)
+static int mcde_dsi_bridge_attach(struct drm_bridge *bridge,
+				  enum drm_bridge_attach_flags flags)
 {
 	struct mcde_dsi *d = bridge_to_mcde_dsi(bridge);
 	struct drm_device *drm = bridge->dev;
···
 	}
 
 	/* Attach the DSI bridge to the output (panel etc) bridge */
-	ret = drm_bridge_attach(bridge->encoder, d->bridge_out, bridge);
+	ret = drm_bridge_attach(bridge->encoder, d->bridge_out, bridge, flags);
 	if (ret) {
 		dev_err(d->dev, "failed to attach the DSI bridge\n");
 		return ret;

drivers/gpu/drm/mediatek/mtk_dpi.c

···
 	/* Currently DPI0 is fixed to be driven by OVL1 */
 	dpi->encoder.possible_crtcs = BIT(1);
 
-	ret = drm_bridge_attach(&dpi->encoder, dpi->bridge, NULL);
+	ret = drm_bridge_attach(&dpi->encoder, dpi->bridge, NULL, 0);
 	if (ret) {
 		dev_err(dev, "Failed to attach bridge: %d\n", ret);
 		goto err_cleanup;

drivers/gpu/drm/mediatek/mtk_dsi.c

···
 
 	/* If there's a bridge, attach to it and let it create the connector */
 	if (dsi->bridge) {
-		ret = drm_bridge_attach(&dsi->encoder, dsi->bridge, NULL);
+		ret = drm_bridge_attach(&dsi->encoder, dsi->bridge, NULL, 0);
 		if (ret) {
 			DRM_ERROR("Failed to attach bridge to drm\n");
 			goto err_encoder_cleanup;

drivers/gpu/drm/mediatek/mtk_hdmi.c

···
  * Bridge callbacks
  */
 
-static int mtk_hdmi_bridge_attach(struct drm_bridge *bridge)
+static int mtk_hdmi_bridge_attach(struct drm_bridge *bridge,
+				  enum drm_bridge_attach_flags flags)
 {
 	struct mtk_hdmi *hdmi = hdmi_ctx_from_bridge(bridge);
 	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	ret = drm_connector_init_with_ddc(bridge->encoder->dev, &hdmi->conn,
 					  &mtk_hdmi_connector_funcs,
···
 
 	if (hdmi->next_bridge) {
 		ret = drm_bridge_attach(bridge->encoder, hdmi->next_bridge,
-					bridge);
+					bridge, flags);
 		if (ret) {
 			dev_err(hdmi->dev,
 				"Failed to attach external bridge: %d\n", ret);

drivers/gpu/drm/msm/dsi/dsi_manager.c

···
 	bridge = &dsi_bridge->base;
 	bridge->funcs = &dsi_mgr_bridge_funcs;
 
-	ret = drm_bridge_attach(encoder, bridge, NULL);
+	ret = drm_bridge_attach(encoder, bridge, NULL, 0);
 	if (ret)
 		goto fail;
 
···
 	encoder = msm_dsi->encoder;
 
 	/* link the internal dsi bridge to the external bridge */
-	drm_bridge_attach(encoder, ext_bridge, int_bridge);
+	drm_bridge_attach(encoder, ext_bridge, int_bridge, 0);
 
 	/*
 	 * we need the drm_connector created by the external bridge

drivers/gpu/drm/msm/edp/edp.c

···
 		goto fail;
 	}
 
-	ret = drm_bridge_attach(encoder, edp->bridge, NULL);
+	ret = drm_bridge_attach(encoder, edp->bridge, NULL, 0);
 	if (ret)
 		goto fail;
 

drivers/gpu/drm/msm/edp/edp_bridge.c

···
 	bridge = &edp_bridge->base;
 	bridge->funcs = &edp_bridge_funcs;
 
-	ret = drm_bridge_attach(edp->encoder, bridge, NULL);
+	ret = drm_bridge_attach(edp->encoder, bridge, NULL, 0);
 	if (ret)
 		goto fail;
 

drivers/gpu/drm/msm/hdmi/hdmi.c

···
 		goto fail;
 	}
 
-	ret = drm_bridge_attach(encoder, hdmi->bridge, NULL);
+	ret = drm_bridge_attach(encoder, hdmi->bridge, NULL, 0);
 	if (ret)
 		goto fail;
 

drivers/gpu/drm/msm/hdmi/hdmi_bridge.c

···
 	bridge = &hdmi_bridge->base;
 	bridge->funcs = &msm_hdmi_bridge_funcs;
 
-	ret = drm_bridge_attach(hdmi->encoder, bridge, NULL);
+	ret = drm_bridge_attach(hdmi->encoder, bridge, NULL, 0);
 	if (ret)
 		goto fail;
 

drivers/gpu/drm/omapdrm/omap_drv.c

···
 
 		if (pipe->output->bridge) {
 			ret = drm_bridge_attach(pipe->encoder,
-						pipe->output->bridge, NULL);
+						pipe->output->bridge, NULL, 0);
 			if (ret < 0)
 				return ret;
 		}

drivers/gpu/drm/rcar-du/rcar_du_encoder.c

···
 	 * Attach the bridge to the encoder. The bridge will create the
 	 * connector.
 	 */
-	ret = drm_bridge_attach(encoder, bridge, NULL);
+	ret = drm_bridge_attach(encoder, bridge, NULL, 0);
 	if (ret) {
 		drm_encoder_cleanup(encoder);
 		return ret;

drivers/gpu/drm/rcar-du/rcar_lvds.c

···
 #include <drm/drm_bridge.h>
 #include <drm/drm_of.h>
 #include <drm/drm_panel.h>
+#include <drm/drm_print.h>
 #include <drm/drm_probe_helper.h>
 
 #include "rcar_lvds.h"
···
 	return true;
 }
 
-static int rcar_lvds_attach(struct drm_bridge *bridge)
+static int rcar_lvds_attach(struct drm_bridge *bridge,
+			    enum drm_bridge_attach_flags flags)
 {
 	struct rcar_lvds *lvds = bridge_to_rcar_lvds(bridge);
 	struct drm_connector *connector = &lvds->connector;
···
 	/* If we have a next bridge just attach it. */
 	if (lvds->next_bridge)
 		return drm_bridge_attach(bridge->encoder, lvds->next_bridge,
-					 bridge);
+					 bridge, flags);
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
+		DRM_ERROR("Fix bridge driver to make connector optional!");
+		return -EINVAL;
+	}
 
 	/* Otherwise if we have a panel, create a connector. */
 	if (!lvds->panel)

drivers/gpu/drm/rockchip/rockchip_lvds.c

···
 			goto err_free_connector;
 		}
 	} else {
-		ret = drm_bridge_attach(encoder, lvds->bridge, NULL);
+		ret = drm_bridge_attach(encoder, lvds->bridge, NULL, 0);
 		if (ret) {
 			DRM_DEV_ERROR(drm_dev->dev,
 				      "failed to attach bridge: %d\n", ret);

drivers/gpu/drm/rockchip/rockchip_rgb.c

···
 
 	rgb->bridge = bridge;
 
-	ret = drm_bridge_attach(encoder, rgb->bridge, NULL);
+	ret = drm_bridge_attach(encoder, rgb->bridge, NULL, 0);
 	if (ret) {
 		DRM_DEV_ERROR(drm_dev->dev,
 			      "failed to attach bridge: %d\n", ret);

drivers/gpu/drm/sti/sti_dvo.c

···
 	bridge->of_node = dvo->dev.of_node;
 	drm_bridge_add(bridge);
 
-	err = drm_bridge_attach(encoder, bridge, NULL);
+	err = drm_bridge_attach(encoder, bridge, NULL, 0);
 	if (err) {
 		DRM_ERROR("Failed to attach bridge\n");
 		return err;

drivers/gpu/drm/sti/sti_hda.c

···
 
 	bridge->driver_private = hda;
 	bridge->funcs = &sti_hda_bridge_funcs;
-	drm_bridge_attach(encoder, bridge, NULL);
+	drm_bridge_attach(encoder, bridge, NULL, 0);
 
 	connector->encoder = encoder;
 

drivers/gpu/drm/sti/sti_hdmi.c

···
 
 	bridge->driver_private = hdmi;
 	bridge->funcs = &sti_hdmi_bridge_funcs;
-	drm_bridge_attach(encoder, bridge, NULL);
+	drm_bridge_attach(encoder, bridge, NULL, 0);
 
 	connector->encoder = encoder;
 

drivers/gpu/drm/stm/ltdc.c

···
 
 	drm_encoder_helper_add(encoder, &ltdc_encoder_helper_funcs);
 
-	ret = drm_bridge_attach(encoder, bridge, NULL);
+	ret = drm_bridge_attach(encoder, bridge, NULL, 0);
 	if (ret) {
 		drm_encoder_cleanup(encoder);
 		return -EINVAL;

drivers/gpu/drm/sun4i/sun4i_lvds.c

···
 	}
 
 	if (bridge) {
-		ret = drm_bridge_attach(encoder, bridge, NULL);
+		ret = drm_bridge_attach(encoder, bridge, NULL, 0);
 		if (ret) {
 			dev_err(drm->dev, "Couldn't attach our bridge\n");
 			goto err_cleanup_connector;

drivers/gpu/drm/sun4i/sun4i_rgb.c

···
 	}
 
 	if (rgb->bridge) {
-		ret = drm_bridge_attach(encoder, rgb->bridge, NULL);
+		ret = drm_bridge_attach(encoder, rgb->bridge, NULL, 0);
 		if (ret) {
 			dev_err(drm->dev, "Couldn't attach our bridge\n");
 			goto err_cleanup_connector;

drivers/gpu/drm/tidss/tidss_kms.c

···
 			return PTR_ERR(enc);
 		}
 
-		ret = drm_bridge_attach(enc, pipes[i].bridge, NULL);
+		ret = drm_bridge_attach(enc, pipes[i].bridge, NULL, 0);
 		if (ret) {
 			dev_err(tidss->dev, "bridge attach failed: %d\n", ret);
 			return ret;

drivers/gpu/drm/tilcdc/tilcdc_external.c

···
 
 	priv->external_encoder->possible_crtcs = BIT(0);
 
-	ret = drm_bridge_attach(priv->external_encoder, bridge, NULL);
+	ret = drm_bridge_attach(priv->external_encoder, bridge, NULL, 0);
 	if (ret) {
 		dev_err(ddev->dev, "drm_bridge_attach() failed %d\n", ret);
 		return ret;

drivers/gpu/drm/vc4/vc4_dpi.c

···
 		bridge = drm_panel_bridge_add_typed(panel,
 						    DRM_MODE_CONNECTOR_DPI);
 
-	return drm_bridge_attach(dpi->encoder, bridge, NULL);
+	return drm_bridge_attach(dpi->encoder, bridge, NULL, 0);
 }
 
 static int vc4_dpi_bind(struct device *dev, struct device *master, void *data)

drivers/gpu/drm/vc4/vc4_dsi.c

···
 			 DRM_MODE_ENCODER_DSI, NULL);
 	drm_encoder_helper_add(dsi->encoder, &vc4_dsi_encoder_helper_funcs);
 
-	ret = drm_bridge_attach(dsi->encoder, dsi->bridge, NULL);
+	ret = drm_bridge_attach(dsi->encoder, dsi->bridge, NULL, 0);
 	if (ret) {
 		dev_err(dev, "bridge attach failed: %d\n", ret);
 		return ret;

include/drm/drm_bridge.h

···
 struct i2c_adapter;
 
 /**
+ * enum drm_bridge_attach_flags - Flags for &drm_bridge_funcs.attach
+ */
+enum drm_bridge_attach_flags {
+	/**
+	 * @DRM_BRIDGE_ATTACH_NO_CONNECTOR: When this flag is set the bridge
+	 * shall not create a drm_connector.
+	 */
+	DRM_BRIDGE_ATTACH_NO_CONNECTOR = BIT(0),
+};
+
+/**
  * struct drm_bridge_funcs - drm_bridge control functions
  */
 struct drm_bridge_funcs {
···
 	 * @attach:
 	 *
 	 * This callback is invoked whenever our bridge is being attached to a
-	 * &drm_encoder.
+	 * &drm_encoder. The flags argument tunes the behaviour of the attach
+	 * operation (see DRM_BRIDGE_ATTACH_*).
 	 *
 	 * The @attach callback is optional.
 	 *
···
 	 *
 	 * Zero on success, error code on failure.
 	 */
-	int (*attach)(struct drm_bridge *bridge);
+	int (*attach)(struct drm_bridge *bridge,
+		      enum drm_bridge_attach_flags flags);
 
 	/**
 	 * @detach:
···
 void drm_bridge_remove(struct drm_bridge *bridge);
 struct drm_bridge *of_drm_find_bridge(struct device_node *np);
 int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
-		      struct drm_bridge *previous);
+		      struct drm_bridge *previous,
+		      enum drm_bridge_attach_flags flags);
 
 /**
  * drm_bridge_get_next_bridge() - Get the next bridge in the chain