[PATCH 2/9] media: rzg2l-cru: csi2: Add device_link from CSI-2 to sensor

[Tommaso Merciai]

The CSI-2 receiver depends on its remote sensor being powered and
configured before it can receive data. Without an explicit device_link
the PM core has no knowledge of this dependency and may suspend the
sensor while CSI-2 is still active, or resume CSI-2 before the sensor
is ready.

Add a DL_FLAG_STATELESS device_link from the CSI-2 device to the sensor
device when the sensor subdev binds. This instructs the PM core to
suspend CSI-2 before the sensor and to resume the sensor before CSI-2.
The link is deleted on unbind.

Move csi2->remote_source assignment to the end of the function.

Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@xxxxxxxxxxxxxx>
---
 .../platform/renesas/rzg2l-cru/rzg2l-csi2.c   | 24 +++++++++++++++----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-csi2.c b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-csi2.c
index 6dc4b53607b4..3a4bc4ef72fc 100644
--- a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-csi2.c
+++ b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-csi2.c
@@ -773,15 +773,28 @@ static int rzg2l_csi2_notify_bound(struct v4l2_async_notifier *notifier,
 				   struct v4l2_async_connection *asd)
 {
 	struct rzg2l_csi2 *csi2 = notifier_to_csi2(notifier);
+	int ret;
 
-	csi2->remote_source = subdev;
+	if (!device_link_add(csi2->dev, subdev->dev, DL_FLAG_STATELESS)) {
+		dev_err(csi2->dev, "Failed to create device link to sensor %s\n",
+			subdev->name);
+		return -EINVAL;
+	}
 
 	dev_dbg(csi2->dev, "Bound subdev: %s pad\n", subdev->name);
 
-	return media_create_pad_link(&subdev->entity, RZG2L_CSI2_SINK,
-				     &csi2->subdev.entity, 0,
-				     MEDIA_LNK_FL_ENABLED |
-				     MEDIA_LNK_FL_IMMUTABLE);
+	ret = media_create_pad_link(&subdev->entity, RZG2L_CSI2_SINK,
+				    &csi2->subdev.entity, 0,
+				    MEDIA_LNK_FL_ENABLED |
+				    MEDIA_LNK_FL_IMMUTABLE);
+	if (ret) {
+		device_link_remove(csi2->dev, subdev->dev);
+		return ret;
+	}
+
+	csi2->remote_source = subdev;
+
+	return 0;
 }
 
 static void rzg2l_csi2_notify_unbind(struct v4l2_async_notifier *notifier,
@@ -790,6 +803,7 @@ static void rzg2l_csi2_notify_unbind(struct v4l2_async_notifier *notifier,
 {
 	struct rzg2l_csi2 *csi2 = notifier_to_csi2(notifier);
 
+	device_link_remove(csi2->dev, subdev->dev);
 	csi2->remote_source = NULL;
 
 	dev_dbg(csi2->dev, "Unbind subdev %s\n", subdev->name);
-- 
2.54.0