linux-kernel - [PATCH v1 1/1] media: imx: csi: Parse link configuration from fw

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Message-Id: <20250305113802.897087-2-mathis.foerst@mt.com>
Date: Wed,  5 Mar 2025 12:38:02 +0100
From: Mathis Foerst <mathis.foerst@...com>
To: linux-kernel@...r.kernel.org
Cc: Mathis Foerst <mathis.foerst@...com>,
	Steve Longerbeam <slongerbeam@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	linux-media@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	manuel.traut@...com,
	mathis.foerst@...hlke.com
Subject: [PATCH v1 1/1] media: imx: csi: Parse link configuration from fw_node

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@...com>
---
 drivers/staging/media/imx/imx-media-csi.c | 36 ++++++++++++++++++++---
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/media/imx/imx-media-csi.c b/drivers/staging/media/imx/imx-media-csi.c
index 3edbc57be2ca..394a9321a10b 100644
--- a/drivers/staging/media/imx/imx-media-csi.c
+++ b/drivers/staging/media/imx/imx-media-csi.c
@@ -169,6 +169,8 @@ static int csi_get_upstream_mbus_config(struct csi_priv *priv,
 {
 	struct v4l2_subdev *sd, *remote_sd;
 	struct media_pad *remote_pad;
+	struct fwnode_handle *ep_node;
+	struct v4l2_fwnode_endpoint ep = { .bus_type = 0 };
 	int ret;

 	if (!priv->src_sd)
@@ -210,11 +212,37 @@ 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 (ret == -ENOIOCTLCMD) {
+		/*
+		 * If the upstream sd does not implement get_mbus_config,
+		 * try to parse the link configuration from its fw_node
+		 */
+		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 ret;
 }

-- 
2.34.1