drm/sun4i: dsi: Allow binding the host without a panel

Currently, the DSI host blocks binding the display pipeline until the
panel is available. This unnecessarily prevents other display outpus
from working, and adds logspam to dmesg when the panel driver is built
as a module (the component master is unsuccessfully brought up several
times during boot).

Flip the dependency, instead requiring the host to be bound before the
panel is attached. The panel driver provides no functionality outside of
the display pipeline anyway.

Since the panel is now probed after the DRM connector, we need a hotplug
event to turn on the connector after the panel is attached.

This has the added benefit of fixing panel module removal/insertion.
Previously, the panel would be turned off when its module was removed.
But because the connector state was hardcoded, nothing knew to turn the
panel back on when it was re-attached. Now, with hotplug events
available, the connector state will follow the panel module state, and
the panel will be re-enabled properly.

Fixes: 133add5b ("drm/sun4i: Add Allwinner A31 MIPI-DSI controller support")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211072858.30784-3-samuel@sholland.org

drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c

@@ -804,7 +804,10 @@ static struct drm_connector_helper_funcs sun6i_dsi_connector_helper_funcs = {
 static enum drm_connector_status
 sun6i_dsi_connector_detect(struct drm_connector *connector, bool force)
 {
-	return connector_status_connected;
+	struct sun6i_dsi *dsi = connector_to_sun6i_dsi(connector);
+
+	return dsi->panel ? connector_status_connected :
+			    connector_status_disconnected;
 }
 
 static const struct drm_connector_funcs sun6i_dsi_connector_funcs = {
@@ -945,10 +948,15 @@ static int sun6i_dsi_attach(struct mipi_dsi_host *host,
 
 	if (IS_ERR(panel))
 		return PTR_ERR(panel);
+	if (!dsi->drm)
+		return -EPROBE_DEFER;
 
 	dsi->panel = panel;
 	dsi->device = device;
 
+	drm_panel_attach(dsi->panel, &dsi->connector);
+	drm_kms_helper_hotplug_event(dsi->drm);
+
 	dev_info(host->dev, "Attached device %s\n", device->name);
 
 	return 0;
@@ -958,10 +966,14 @@ static int sun6i_dsi_detach(struct mipi_dsi_host *host,
 			    struct mipi_dsi_device *device)
 {
 	struct sun6i_dsi *dsi = host_to_sun6i_dsi(host);
+	struct drm_panel *panel = dsi->panel;
 
 	dsi->panel = NULL;
 	dsi->device = NULL;
 
+	drm_panel_detach(panel);
+	drm_kms_helper_hotplug_event(dsi->drm);
+
 	return 0;
 }
 
@@ -1026,9 +1038,6 @@ static int sun6i_dsi_bind(struct device *dev, struct device *master,
 	struct sun6i_dsi *dsi = dev_get_drvdata(dev);
 	int ret;
 
-	if (!dsi->panel)
-		return -EPROBE_DEFER;
-
 	drm_encoder_helper_add(&dsi->encoder,
 			       &sun6i_dsi_enc_helper_funcs);
 	ret = drm_encoder_init(drm,
@@ -1054,7 +1063,8 @@ static int sun6i_dsi_bind(struct device *dev, struct device *master,
 	}
 
 	drm_connector_attach_encoder(&dsi->connector, &dsi->encoder);
-	drm_panel_attach(dsi->panel, &dsi->connector);
+
+	dsi->drm = drm;
 
 	return 0;
 
@@ -1068,7 +1078,7 @@ static void sun6i_dsi_unbind(struct device *dev, struct device *master,
 {
 	struct sun6i_dsi *dsi = dev_get_drvdata(dev);
 
-	drm_panel_detach(dsi->panel);
+	dsi->drm = NULL;
 }
 
 static const struct component_ops sun6i_dsi_ops = {

drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h

@@ -29,6 +29,7 @@ struct sun6i_dsi {
 
 	struct device		*dev;
 	struct mipi_dsi_device	*device;
+	struct drm_device	*drm;
 	struct drm_panel	*panel;
 };