linux-kernel - [PATCH 1/3] media: videobuf2: Add a transfer error event

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Date:   Thu, 19 May 2022 20:00:07 +0200
From:   Michael Rodin <mrodin@...adit-jv.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-renesas-soc@...r.kernel.org>
CC:     Michael Rodin <mrodin@...adit-jv.com>, <michael@...in.online>,
        <erosca@...adit-jv.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>
Subject: [PATCH 1/3] media: videobuf2: Add a transfer error event

From: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

Add a new V4L2_EVENT_XFER_ERROR event to signal if a unrecoverable error
happens during video transfer.

The use-case that sparked this new event is to signal to the video
device driver that an error has happen on the CSI-2 bus from the CSI-2
receiver subdevice.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
[mrodin@...adit-jv.com: added information what to do if this new event is received]
Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>
---
 Documentation/userspace-api/media/v4l/vidioc-dqevent.rst     | 9 +++++++++
 Documentation/userspace-api/media/videodev2.h.rst.exceptions | 1 +
 include/uapi/linux/videodev2.h                               | 1 +
 3 files changed, 11 insertions(+)

diff --git a/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst b/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst
index 6eb4007..ed0a5ff 100644
--- a/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst
+++ b/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst
@@ -182,6 +182,15 @@ call.
 	the regions changes. This event has a struct
 	:c:type:`v4l2_event_motion_det`
 	associated with it.
+    * - ``V4L2_EVENT_XFER_ERROR``
+      - 7
+      - This event is triggered when an transfer error is detected while
+	streaming. For example if a unrecoverable error is detected on a video
+	bus in the pipeline. If a driver receives this event from an upstream
+	subdevice, it has to check if it is affected by this error and then try
+	to recover from this error. If an internal recovery is not possible,
+	then it can forward the event to userspace so the streaming application
+	has to restart streaming if it wants to continue.
     * - ``V4L2_EVENT_PRIVATE_START``
       - 0x08000000
       - Base event number for driver-private events.
diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
index 9cbb7a0..25bde61 100644
--- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
+++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
@@ -500,6 +500,7 @@ replace define V4L2_EVENT_CTRL event-type
 replace define V4L2_EVENT_FRAME_SYNC event-type
 replace define V4L2_EVENT_SOURCE_CHANGE event-type
 replace define V4L2_EVENT_MOTION_DET event-type
+replace define V4L2_EVENT_XFER_ERROR event-type
 replace define V4L2_EVENT_PRIVATE_START event-type
 
 replace define V4L2_EVENT_CTRL_CH_VALUE ctrl-changes-flags
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 6d465dc..8c75bd8 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -2383,6 +2383,7 @@ struct v4l2_streamparm {
 #define V4L2_EVENT_FRAME_SYNC			4
 #define V4L2_EVENT_SOURCE_CHANGE		5
 #define V4L2_EVENT_MOTION_DET			6
+#define V4L2_EVENT_XFER_ERROR			7
 #define V4L2_EVENT_PRIVATE_START		0x08000000
 
 /* Payload for V4L2_EVENT_VSYNC */
-- 
2.7.4