drm/rockchip: add function to check if endpoint is a subdriver

To be able to have both internal subdrivers and external bridge
drivers as output endpoints of vops, add a function to be able
to distinguish these.

changes in v8:
- improved function documentation
- better error handling
- put calls for node and pdev references
changes in v6:
- added function to check subdriver vs. bridge

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Sandy Huang <hjc@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180830211207.10480-2-heiko@sntech.de

drivers/gpu/drm/rockchip/rockchip_drm_drv.c

@@ -24,6 +24,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/module.h>
 #include <linux/of_graph.h>
+#include <linux/of_platform.h>
 #include <linux/component.h>
 #include <linux/console.h>
 #include <linux/iommu.h>
@@ -267,6 +268,53 @@ static const struct dev_pm_ops rockchip_drm_pm_ops = {
 static struct platform_driver *rockchip_sub_drivers[MAX_ROCKCHIP_SUB_DRIVERS];
 static int num_rockchip_sub_drivers;
 
+/*
+ * Check if a vop endpoint is leading to a rockchip subdriver or bridge.
+ * Should be called from the component bind stage of the drivers
+ * to ensure that all subdrivers are probed.
+ *
+ * @ep: endpoint of a rockchip vop
+ *
+ * returns true if subdriver, false if external bridge and -ENODEV
+ * if remote port does not contain a device.
+ */
+int rockchip_drm_endpoint_is_subdriver(struct device_node *ep)
+{
+	struct device_node *node = of_graph_get_remote_port_parent(ep);
+	struct platform_device *pdev;
+	struct device_driver *drv;
+	int i;
+
+	if (!node)
+		return -ENODEV;
+
+	/* status disabled will prevent creation of platform-devices */
+	pdev = of_find_device_by_node(node);
+	of_node_put(node);
+	if (!pdev)
+		return -ENODEV;
+
+	/*
+	 * All rockchip subdrivers have probed at this point, so
+	 * any device not having a driver now is an external bridge.
+	 */
+	drv = pdev->dev.driver;
+	if (!drv) {
+		platform_device_put(pdev);
+		return false;
+	}
+
+	for (i = 0; i < num_rockchip_sub_drivers; i++) {
+		if (rockchip_sub_drivers[i] == to_platform_driver(drv)) {
+			platform_device_put(pdev);
+			return true;
+		}
+	}
+
+	platform_device_put(pdev);
+	return false;
+}
+
 static int compare_dev(struct device *dev, void *data)
 {
 	return dev == (struct device *)data;

drivers/gpu/drm/rockchip/rockchip_drm_drv.h

@@ -64,6 +64,7 @@ void rockchip_drm_dma_detach_device(struct drm_device *drm_dev,
 				    struct device *dev);
 int rockchip_drm_wait_vact_end(struct drm_crtc *crtc, unsigned int mstimeout);
 
+int rockchip_drm_endpoint_is_subdriver(struct device_node *ep);
 extern struct platform_driver cdn_dp_driver;
 extern struct platform_driver dw_hdmi_rockchip_pltfm_driver;
 extern struct platform_driver dw_mipi_dsi_driver;