drm/msm/hdmi: support attaching the "next" bridge

There might be a chain of bridges attached to the HDMI node
(including but not limited to the display-connector bridge). Add support
for attaching them right to the HDMI bridge chain.
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/489709/
Link: https://lore.kernel.org/r/20220616085057.432353-1-dmitry.baryshkov@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

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

@@ -9,6 +9,7 @@
 #include <linux/of_gpio.h>
 
 #include <drm/drm_bridge_connector.h>
+#include <drm/drm_of.h>
 
 #include <sound/hdmi-codec.h>
 #include "hdmi.h"
@@ -133,6 +134,10 @@ static struct hdmi *msm_hdmi_init(struct platform_device *pdev)
 	hdmi->config = config;
 	spin_lock_init(&hdmi->reg_lock);
 
+	ret = drm_of_find_panel_or_bridge(pdev->dev.of_node, 1, 0, NULL, &hdmi->next_bridge);
+	if (ret && ret != -ENODEV)
+		goto fail;
+
 	hdmi->mmio = msm_ioremap(pdev, config->mmio_name);
 	if (IS_ERR(hdmi->mmio)) {
 		ret = PTR_ERR(hdmi->mmio);
@@ -308,6 +313,15 @@ int msm_hdmi_modeset_init(struct hdmi *hdmi,
 		goto fail;
 	}
 
+	if (hdmi->next_bridge) {
+		ret = drm_bridge_attach(hdmi->encoder, hdmi->next_bridge, hdmi->bridge,
+					DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+		if (ret) {
+			DRM_DEV_ERROR(dev->dev, "failed to attach next HDMI bridge: %d\n", ret);
+			goto fail;
+		}
+	}
+
 	hdmi->connector = drm_bridge_connector_init(hdmi->dev, encoder);
 	if (IS_ERR(hdmi->connector)) {
 		ret = PTR_ERR(hdmi->connector);

drivers/gpu/drm/msm/hdmi/hdmi.h

@@ -62,6 +62,8 @@ struct hdmi {
 	struct drm_connector *connector;
 	struct drm_bridge *bridge;
 
+	struct drm_bridge *next_bridge;
+
 	/* the encoder we are hooked to (outside of hdmi block) */
 	struct drm_encoder *encoder;