[PATCH v2 02/12] drm: bridge: samsung-dsim: Lookup OF-graph or Child node devices

[Jagan Teki <jagan@amarulasolutions.com>]

The child devices in MIPI DSI can be binding with OF-graph
and also via child nodes.

The OF-graph interface represents the child devices via
remote and associated endpoint numbers like

dsi {
   compatible = "fsl,imx8mm-mipi-dsim";

   ports {
	port@0 {
	     reg = <0>;

	     dsi_in_lcdif: endpoint@0 {
		  reg = <0>;
		  remote-endpoint = <&lcdif_out_dsi>;
	     };
	};

	port@1 {
	     reg = <1>;

	     dsi_out_bridge: endpoint {
		  remote-endpoint = <&bridge_in_dsi>;
	     };
	};
};

The child node interface represents the child devices via
conventional child nodes on given DSI parent like

dsi {
   compatible = "samsung,exynos5433-mipi-dsi";

   ports {
        port@0 {
             reg = <0>;

             dsi_to_mic: endpoint {
                  remote-endpoint = <&mic_to_dsi>;
             };
        };
   };

   panel@0 {
        reg = <0>;
   };
};

As Samsung DSIM bridge is common DSI IP across all Exynos DSI
and NXP i.MX8M host controllers, this patch adds support to
lookup the child devices whether its bindings on the associated
host represent OF-graph or child node interfaces.

v2:
* new patch

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
---
 drivers/gpu/drm/bridge/samsung-dsim.c | 38 +++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
index 7745902f3f1e..f23f06d55158 100644
--- a/drivers/gpu/drm/bridge/samsung-dsim.c
+++ b/drivers/gpu/drm/bridge/samsung-dsim.c
@@ -1357,18 +1357,52 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
 	struct samsung_dsim *dsi = host_to_dsi(host);
 	const struct samsung_dsim_plat_data *pdata = dsi->plat_data;
 	struct device *dev = dsi->dev;
+	struct device_node *np = dev->of_node;
+	struct device_node *remote;
 	struct drm_panel *panel;
 	int ret;
 
-	panel = of_drm_find_panel(device->dev.of_node);
+	/**
+	 * Devices can also be child nodes when we also control that device
+	 * through the upstream device (ie, MIPI-DCS for a MIPI-DSI device).
+	 *
+	 * Lookup for a child node of the given parent that isn't either port
+	 * or ports.
+	 */
+	for_each_available_child_of_node(np, remote) {
+		if (of_node_name_eq(remote, "port") ||
+		    of_node_name_eq(remote, "ports"))
+			continue;
+
+		goto of_find_panel_or_bridge;
+	}
+
+	/*
+	 * of_graph_get_remote_node() produces a noisy error message if port
+	 * node isn't found and the absence of the port is a legit case here,
+	 * so at first we silently check whether graph presents in the
+	 * device-tree node.
+	 */
+	if (!of_graph_is_present(np))
+		return -ENODEV;
+
+	remote = of_graph_get_remote_node(np, 1, 0);
+
+of_find_panel_or_bridge:
+	if (!remote)
+		return -ENODEV;
+
+	panel = of_drm_find_panel(remote);
 	if (!IS_ERR(panel)) {
 		dsi->out_bridge = devm_drm_panel_bridge_add(dev, panel);
 	} else {
-		dsi->out_bridge = of_drm_find_bridge(device->dev.of_node);
+		dsi->out_bridge = of_drm_find_bridge(remote);
 		if (!dsi->out_bridge)
 			dsi->out_bridge = ERR_PTR(-EINVAL);
 	}
 
+	of_node_put(remote);
+
 	if (IS_ERR(dsi->out_bridge)) {
 		ret = PTR_ERR(dsi->out_bridge);
 		DRM_DEV_ERROR(dev, "failed to find the bridge: %d\n", ret);
-- 
2.25.1