[PATCH 2/3] drm/msm: dsi host: Use device graph parsing to parse connected panel

[Archit Taneja]

The dsi host looks for the connected panel node by parsing for a child
named 'panel'. This hierarchy isn't very flexible. The connected
panel is forced to be a child to the dsi host, and hence, a mipi dsi
device. This isn't suitable for dsi devices that don't use mipi dsi
as their control bus.

Follow the of_graph approach of creating ports and endpoints to
represent the connections between the dsi host and the panel connected
to it. In our case, the dsi host will only have one output port, linked
to the panel's input port.

Update DT binding documentation with device graph usage info.

Signed-off-by: Archit Taneja <architt@xxxxxxxxxxxxxx>
---
 Documentation/devicetree/bindings/drm/msm/dsi.txt | 15 ++++++
 drivers/gpu/drm/msm/dsi/dsi_host.c                | 64 +++++++++++++++++------
 2 files changed, 63 insertions(+), 16 deletions(-)

diff --git a/Documentation/devicetree/bindings/drm/msm/dsi.txt b/Documentation/devicetree/bindings/drm/msm/dsi.txt
index 6ccd860..c88ec3c 100644
--- a/Documentation/devicetree/bindings/drm/msm/dsi.txt
+++ b/Documentation/devicetree/bindings/drm/msm/dsi.txt
@@ -25,6 +25,9 @@ Required properties:
 - vddio-supply: phandle to vdd-io regulator device node
 - vdda-supply: phandle to vdda regulator device node
 - qcom,dsi-phy: phandle to DSI PHY device node
+- port: DSI controller output port. This contains one endpoint subnode, with its
+  remote-endpoint set to the phandle of the connected panel's endpoint.
+  See Documentation/devicetree/bindings/graph.txt for device graph info.
 
 Optional properties:
 - panel@0: Node of panel connected to this DSI controller.
@@ -101,6 +104,18 @@ Example:
 
 			power-supply = <...>;
 			backlight = <...>;
+
+			port {
+				panel_in: endpoint {
+					remote-endpoint = <&dsi0_out>;
+				};
+			};
+		};
+
+		port {
+			dsi0_out: endpoint {
+				remote-endpoint = <&panel_in>;
+			};
 		};
 	};
 
diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 1751659..ab0b23b 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -20,6 +20,7 @@
 #include <linux/of_device.h>
 #include <linux/of_gpio.h>
 #include <linux/of_irq.h>
+#include <linux/of_graph.h>
 #include <linux/regulator/consumer.h>
 #include <linux/spinlock.h>
 #include <video/mipi_display.h>
@@ -1379,7 +1380,7 @@ static int dsi_host_attach(struct mipi_dsi_host *host,
 	msm_host->format = dsi->format;
 	msm_host->mode_flags = dsi->mode_flags;
 
-	msm_host->panel_node = dsi->dev.of_node;
+	WARN_ON(dsi->dev.of_node != msm_host->panel_node);
 
 	/* Some gpios defined in panel DT need to be controlled by host */
 	ret = dsi_host_init_panel_gpios(msm_host, &dsi->dev);
@@ -1429,6 +1430,46 @@ static struct mipi_dsi_host_ops dsi_host_ops = {
 	.transfer = dsi_host_transfer,
 };
 
+static int msm_dsi_host_parse_dt(struct msm_dsi_host *msm_host)
+{
+	struct device *dev = &msm_host->pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct device_node *endpoint, *panel_node;
+	int ret;
+
+	ret = of_property_read_u32(np, "qcom,dsi-host-index", &msm_host->id);
+	if (ret) {
+		dev_err(dev, "%s: host index not specified, ret=%d\n",
+			__func__, ret);
+		return ret;
+	}
+
+	/*
+	 * get the first endpoint node. in our case, dsi has one output port
+	 * to which the panel is connected.
+	 */
+	endpoint = of_graph_get_next_endpoint(np, NULL);
+	if (IS_ERR(endpoint)) {
+		dev_err(dev, "%s: no valid endpoint\n", __func__);
+		return PTR_ERR(endpoint);
+	}
+
+	of_node_put(endpoint);
+
+	/* get panel node from the output port's endpoint data */
+	panel_node = of_graph_get_remote_port_parent(endpoint);
+	if (IS_ERR(panel_node)) {
+		dev_err(dev, "%s: no valid device\n", __func__);
+		return PTR_ERR(panel_node);
+	}
+
+	of_node_put(panel_node);
+
+	msm_host->panel_node = panel_node;
+
+	return 0;
+}
+
 int msm_dsi_host_init(struct msm_dsi *msm_dsi)
 {
 	struct msm_dsi_host *msm_host = NULL;
@@ -1443,15 +1484,13 @@ int msm_dsi_host_init(struct msm_dsi *msm_dsi)
 		goto fail;
 	}
 
-	ret = of_property_read_u32(pdev->dev.of_node,
-				"qcom,dsi-host-index", &msm_host->id);
+	msm_host->pdev = pdev;
+
+	ret = msm_dsi_host_parse_dt(msm_host);
 	if (ret) {
-		dev_err(&pdev->dev,
-			"%s: host index not specified, ret=%d\n",
-			__func__, ret);
+		pr_err("%s: failed to parse dt\n", __func__);
 		goto fail;
 	}
-	msm_host->pdev = pdev;
 
 	ret = dsi_clk_init(msm_host);
 	if (ret) {
@@ -1559,7 +1598,6 @@ int msm_dsi_host_modeset_init(struct mipi_dsi_host *host,
 int msm_dsi_host_register(struct mipi_dsi_host *host, bool check_defer)
 {
 	struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
-	struct device_node *node;
 	int ret;
 
 	/* Register mipi dsi host */
@@ -1579,14 +1617,8 @@ int msm_dsi_host_register(struct mipi_dsi_host *host, bool check_defer)
 		 * create framebuffer.
 		 */
 		if (check_defer) {
-			node = of_get_child_by_name(msm_host->pdev->dev.of_node,
-							"panel");
-			if (node) {
-				of_node_put(node);
-
-				if (!of_drm_find_panel(node))
-					return -EPROBE_DEFER;
-			}
+			if (!of_drm_find_panel(msm_host->panel_node))
+				return -EPROBE_DEFER;
 		}
 	}
 
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