media: mipi-csis: Emit V4L2_EVENT_FRAME_SYNC events

The Samsung CSIS MIPI receiver provides a start-of-frame interrupt and
a framecount register. As the CSI receiver is the hardware unit that lies
closest to the sensor, the frame counter is the best we can get on these
devices. In case of the ISI available on the i.MX8 M Plus it is also the
only native start-of-frame signal available.

This patch exposes the sof interrupt and the framecount as
V4L2_EVENT_FRAME_SYNC event on the subdevice.

It was tested on a Debix-Som-A with a 6.8-rc4 kernel.

Reviewed-by: Laurent Pinchart <[e-mail]>
Reviewed-by: Jacopo Mondi <[e-mail]>
Reviewed-by: Umang Jain <[e-mail]>
Signed-off-by: Stefan Klug <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Laurent Pinchart <[e-mail]>

drivers/media/platform/nxp/imx-mipi-csis.c

···
 
 #include <media/v4l2-common.h>
 #include <media/v4l2-device.h>
+#include <media/v4l2-event.h>
 #include <media/v4l2-fwnode.h>
 #include <media/v4l2-mc.h>
 #include <media/v4l2-subdev.h>
···
 	mipi_csis_system_enable(csis, false);
 }
 
+static void mipi_csis_queue_event_sof(struct mipi_csis_device *csis)
+{
+	struct v4l2_event event = {
+		.type = V4L2_EVENT_FRAME_SYNC,
+	};
+	u32 frame;
+
+	frame = mipi_csis_read(csis, MIPI_CSIS_FRAME_COUNTER_CH(0));
+	event.u.frame_sync.frame_sequence = frame;
+	v4l2_event_queue(csis->sd.devnode, &event);
+}
+
 static irqreturn_t mipi_csis_irq_handler(int irq, void *dev_id)
 {
 	struct mipi_csis_device *csis = dev_id;
···
 				event->counter++;
 		}
 	}
+
+	if (status & MIPI_CSIS_INT_SRC_FRAME_START)
+		mipi_csis_queue_event_sof(csis);
+
 	spin_unlock_irqrestore(&csis->slock, flags);
 
 	mipi_csis_write(csis, MIPI_CSIS_INT_SRC, status);
···
 	return 0;
 }
 
+static int mipi_csis_subscribe_event(struct v4l2_subdev *sd, struct v4l2_fh *fh,
+				     struct v4l2_event_subscription *sub)
+{
+	if (sub->type != V4L2_EVENT_FRAME_SYNC)
+		return -EINVAL;
+
+	/* V4L2_EVENT_FRAME_SYNC doesn't require an id, so zero should be set */
+	if (sub->id != 0)
+		return -EINVAL;
+
+	return v4l2_event_subscribe(fh, sub, 0, NULL);
+}
+
 static const struct v4l2_subdev_core_ops mipi_csis_core_ops = {
 	.log_status	= mipi_csis_log_status,
+	.subscribe_event =  mipi_csis_subscribe_event,
+	.unsubscribe_event = v4l2_event_subdev_unsubscribe,
 };
 
 static const struct v4l2_subdev_video_ops mipi_csis_video_ops = {
···
 	snprintf(sd->name, sizeof(sd->name), "csis-%s",
 		 dev_name(csis->dev));
 
-	sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
+	sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE | V4L2_SUBDEV_FL_HAS_EVENTS;
 	sd->ctrl_handler = NULL;
 
 	sd->entity.function = MEDIA_ENT_F_VID_IF_BRIDGE;