[media] v4l: vb2: Add fatal error condition flag

When a fatal error occurs that render the device unusable, the only
options for a driver to signal the error condition to userspace is to
set the V4L2_BUF_FLAG_ERROR flag when dequeuing buffers and to return an
error from the buffer prepare handler when queuing buffers.

The buffer error flag indicates a transient error and can't be used by
applications to detect fatal errors. Returning an error from vb2_qbuf()
is thus the only real indication that a fatal error occurred. However,
this is difficult to handle for multithreaded applications that requeue
buffers from a thread other than the control thread. In particular the
poll() call in the control thread will not notify userspace of the
error.

This patch adds an explicit mechanism to report fatal errors to
userspace. Drivers can call the vb2_queue_error() function to signal a
fatal error. From this moment on, buffer preparation will return -EIO to
userspace, and vb2_poll() will set the POLLERR flag and return
immediately. The error flag is cleared when cancelling the queue, either
at stream off time (through vb2_streamoff) or when releasing the queue
with vb2_queue_release().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 8fab6fa0dbfb..1a262aeb1741 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -375,6 +375,7 @@ struct v4l2_fh;
  * @streaming:	current streaming state
  * @start_streaming_called: start_streaming() was called successfully and we
  *		started streaming.
+ * @error:	a fatal error occurred on the queue
  * @fileio:	file io emulator internal data, used only if emulator is active
  * @threadio:	thread io internal data, used only if thread is active
  */
@@ -411,6 +412,7 @@ struct vb2_queue {
 
 	unsigned int			streaming:1;
 	unsigned int			start_streaming_called:1;
+	unsigned int			error:1;
 
 	struct vb2_fileio_data		*fileio;
 	struct vb2_threadio_data	*threadio;
@@ -444,6 +446,7 @@ int vb2_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b);
 int __must_check vb2_queue_init(struct vb2_queue *q);
 
 void vb2_queue_release(struct vb2_queue *q);
+void vb2_queue_error(struct vb2_queue *q);
 
 int vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b);
 int vb2_expbuf(struct vb2_queue *q, struct v4l2_exportbuffer *eb);