[PATCH v3 1/1] media: imx: csi: Parse link configuration from fw_node

[Mathis Foerst <mathis.foerst@mt.com>]

The imx-media-csi driver requires upstream camera drivers to implement
the subdev-pad-op "get_mbus_config" [0]. Camera drivers that don't
implement this function are not usable on the i.MX6.

The docs for get_mbus_config [1] say:
@get_mbus_config: get the media bus configuration of a remote sub-device.
            The media bus configuration is usually retrieved from the
            firmware interface at sub-device probe time, immediately
            applied to the hardware and eventually adjusted by the
            driver.

Currently, the imx-media-csi driver is not incorporating the information
from the firmware interface and therefore relies on the implementation of
get_mbus_config by the camera driver.

To be compatible with camera drivers not implementing get_mbus_config
(which is the usual case), use the bus information from the fw interface:

The camera does not necessarily has a direct media bus link to the CSI as
the video-mux and/or the MIPI CSI-2 receiver of the i.MX6 might be in
between them on the media pipeline.
The CSI driver already implements the functionality to find the connected
camera sub-device to call get_mbus_config on it.

At this point the driver is modified as follows:
In the case that get_mbus_config is not implemented by the upstream
camera, try to get its endpoint configuration from the firmware interface
usign v4l2_fwnode_endpoint_parse.
For the supported mbus_types (V4L2_MBUS_PARALLEL, V4L2_MBUS_BT656 and
V4L2_MBUS_CSI2_DPHY), extract the mbus_config from the endpoint
configuration.
For all other mbus_types, return an error.

Note that parsing the mbus_config from the fw interface is not done during
probing because the camera that's connected to the CSI can change based on
the selected input of the video-mux at runtime.

[0] drivers/staging/media/imx/imx-media-csi.c - line 211..216
[1] include/media/v4l2-subdev.h - line 814

Signed-off-by: Mathis Foerst <mathis.foerst@mt.com>
---
 drivers/staging/media/imx/imx-media-csi.c | 45 +++++++++++++++++++++--
 1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
index 3edbc57be2ca..e642b4cc6182 100644
--- a/drivers/staging/media/imx/imx-media-csi.c
+++ b/drivers/staging/media/imx/imx-media-csi.c
@@ -158,6 +158,42 @@ static inline bool requires_passthrough(struct v4l2_mbus_config *mbus_cfg,
 		 infmt->code != MEDIA_BUS_FMT_YUYV8_2X8);
 }
 
+static int csi_parse_upstream_fw_link_config(struct csi_priv *priv,
+					     struct v4l2_subdev *remote_sd,
+					     struct v4l2_mbus_config *mbus_cfg)
+{
+	struct fwnode_handle *ep_node;
+	struct v4l2_fwnode_endpoint ep = { .bus_type = V4L2_MBUS_UNKNOWN };
+	int ret;
+
+	ep_node = fwnode_graph_get_endpoint_by_id(dev_fwnode(remote_sd->dev),
+						  0, 0,
+						  FWNODE_GRAPH_ENDPOINT_NEXT);
+	if (!ep_node)
+		return -ENOTCONN;
+
+	ret = v4l2_fwnode_endpoint_parse(ep_node, &ep);
+	fwnode_handle_put(ep_node);
+	if (ret)
+		return ret;
+
+	mbus_cfg->type = ep.bus_type;
+	switch (ep.bus_type) {
+	case V4L2_MBUS_PARALLEL:
+	case V4L2_MBUS_BT656:
+		mbus_cfg->bus.parallel = ep.bus.parallel;
+		break;
+	case V4L2_MBUS_CSI2_DPHY:
+		mbus_cfg->bus.mipi_csi2 = ep.bus.mipi_csi2;
+		break;
+	default:
+		v4l2_err(&priv->sd, "Unsupported mbus_type: %i\n",
+			 ep.bus_type);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 /*
  * Queries the media bus config of the upstream entity that provides data to
  * the CSI. This will either be the entity directly upstream from the CSI-2
@@ -211,9 +247,12 @@ static int csi_get_upstream_mbus_config(struct csi_priv *priv,
 	ret = v4l2_subdev_call(remote_sd, pad, get_mbus_config,
 			       remote_pad->index, mbus_cfg);
 	if (ret == -ENOIOCTLCMD)
-		v4l2_err(&priv->sd,
-			 "entity %s does not implement get_mbus_config()\n",
-			 remote_pad->entity->name);
+		/*
+		 * If the upstream sd does not implement get_mbus_config,
+		 * try to parse the link configuration from its fw_node
+		 */
+		ret = csi_parse_upstream_fw_link_config(priv, remote_sd,
+							mbus_cfg);
 
 	return ret;
 }
-- 
2.34.1