@@ -2409,6 +2409,22 @@ struct vb2_fileio_buf {
/**
* struct vb2_fileio_data - queue context used by file io emulator
*
+ * @cur_index: the index of the buffer currently being read from or
+ * written to. If equal to q->num_buffers then a new buffer
+ * must be dequeued.
+ * @initial_index: in the read() case all buffers are queued up immediately
+ * in __vb2_init_fileio() and __vb2_perform_fileio() just cycles
+ * buffers. However, in the write() case no buffers are initially
+ * queued, instead whenever a buffer is full it is queued up by
+ * __vb2_perform_fileio(). Only once all available buffers have
+ * been queued up will __vb2_perform_fileio() start to dequeue
+ * buffers. This means that initially __vb2_perform_fileio()
+ * needs to know what buffer index to use when it is queuing up
+ * the buffers for the first time. That initial index is stored
+ * in this field. Once it is equal to q->num_buffers all
+ * available buffers have been queued and __vb2_perform_fileio()
+ * should start the normal dequeue/queue cycle.
+ *
* vb2 provides a compatibility layer and emulator of file io (read and
* write) calls on top of streaming API. For proper operation it required
* this structure to save the driver state between each call of the read
@@ -2418,7 +2434,8 @@ struct vb2_fileio_data {
struct v4l2_requestbuffers req;
struct v4l2_buffer b;
struct vb2_fileio_buf bufs[VIDEO_MAX_FRAME];
- unsigned int index;
+ unsigned int cur_index;
+ unsigned int initial_index;
unsigned int q_count;
unsigned int dq_count;
unsigned int flags;
@@ -2518,7 +2535,12 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
goto err_reqbufs;
fileio->bufs[i].queued = 1;
}
- fileio->index = q->num_buffers;
+ /*
+ * All buffers have been queued, so mark that by setting
+ * initial_index to q->num_buffers
+ */
+ fileio->initial_index = q->num_buffers;
+ fileio->cur_index = q->num_buffers;
}
/*
@@ -2597,7 +2619,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
/*
* Check if we need to dequeue the buffer.
*/
- index = fileio->index;
+ index = fileio->cur_index;
if (index >= q->num_buffers) {
/*
* Call vb2_dqbuf to get buffer back.
@@ -2611,7 +2633,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
return ret;
fileio->dq_count += 1;
- index = fileio->b.index;
+ fileio->cur_index = index = fileio->b.index;
buf = &fileio->bufs[index];
/*
@@ -2687,8 +2709,20 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
buf->queued = 1;
buf->size = vb2_plane_size(q->bufs[index], 0);
fileio->q_count += 1;
- if (fileio->index < q->num_buffers)
- fileio->index++;
+ /*
+ * If we are queuing up buffers for the first time, then
+ * increase initial_index by one.
+ */
+ if (fileio->initial_index < q->num_buffers)
+ fileio->initial_index++;
+ /*
+ * The next buffer to use is either a buffer that's going to be
+ * queued for the first time (initial_index < q->num_buffers)
+ * or it is equal to q->num_buffers, meaning that the next
+ * time we need to dequeue a buffer since we've now queued up
+ * all the 'first time' buffers.
+ */
+ fileio->cur_index = fileio->initial_index;
}
/*