V4L/DVB (8772): cx18: Convert cx18_queue buffers member to atomic_t

cx18: Convert cx18_queue buffers member to atomic_t.  This allows safe
concurrent access to check if a queue has data without having to acquire the
queue spinlock.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

4 files changed, 11 insertions, 10 deletions

diff --git a/drivers/media/video/cx18/cx18-driver.h b/drivers/media/video/cx18/cx18-driver.h
index 28c490b1b64..8812a5ec635 100644
--- a/drivers/media/video/cx18/cx18-driver.h
+++ b/drivers/media/video/cx18/cx18-driver.h
@@ -216,7 +216,7 @@ struct cx18_buffer {
 
 struct cx18_queue {
         struct list_head list;
-        u32 buffers;
+        atomic_t buffers;
         u32 bytesused;
 };
 
diff --git a/drivers/media/video/cx18/cx18-fileops.c b/drivers/media/video/cx18/cx18-fileops.c
index 2fdbfb994dd..eb0144f9556 100644
--- a/drivers/media/video/cx18/cx18-fileops.c
+++ b/drivers/media/video/cx18/cx18-fileops.c
@@ -223,7 +223,7 @@ static struct cx18_buffer *cx18_get_buffer(struct cx18_stream *s, int non_block,
                 prepare_to_wait(&s->waitq, &wait, TASK_INTERRUPTIBLE);
                 /* New buffers might have become available before we were added
                    to the waitqueue */
-                if (!s->q_full.buffers)
+                if (!atomic_read(&s->q_full.buffers))
                         schedule();
                 finish_wait(&s->waitq, &wait);
                 if (signal_pending(current)) {
@@ -509,7 +509,7 @@ unsigned int cx18_v4l2_enc_poll(struct file *filp, poll_table *wait)
         CX18_DEBUG_HI_FILE("Encoder poll\n");
         poll_wait(filp, &s->waitq, wait);
 
-        if (s->q_full.buffers || s->q_io.buffers)
+        if (atomic_read(&s->q_full.buffers) || atomic_read(&s->q_io.buffers))
                 return POLLIN | POLLRDNORM;
         if (eof)
                 return POLLHUP;
diff --git a/drivers/media/video/cx18/cx18-ioctl.c b/drivers/media/video/cx18/cx18-ioctl.c
index a7f839631d6..5325c7aacaf 100644
--- a/drivers/media/video/cx18/cx18-ioctl.c
+++ b/drivers/media/video/cx18/cx18-ioctl.c
@@ -731,7 +731,8 @@ static int cx18_log_status(struct file *file, void *fh)
                         continue;
                 CX18_INFO("Stream %s: status 0x%04lx, %d%% of %d KiB (%d buffers) in use\n",
                           s->name, s->s_flags,
-                          (s->buffers - s->q_free.buffers) * 100 / s->buffers,
+                          (s->buffers - atomic_read(&s->q_free.buffers))
+                                * 100 / s->buffers,
                           (s->buffers * s->buf_size) / 1024, s->buffers);
         }
         CX18_INFO("Read MPEG/VBI: %lld/%lld bytes\n",
diff --git a/drivers/media/video/cx18/cx18-queue.c b/drivers/media/video/cx18/cx18-queue.c
index 4f3bd43ba80..a33ba04a268 100644
--- a/drivers/media/video/cx18/cx18-queue.c
+++ b/drivers/media/video/cx18/cx18-queue.c
@@ -37,7 +37,7 @@ void cx18_buf_swap(struct cx18_buffer *buf)
 void cx18_queue_init(struct cx18_queue *q)
 {
         INIT_LIST_HEAD(&q->list);
-        q->buffers = 0;
+        atomic_set(&q->buffers, 0);
         q->bytesused = 0;
 }
 
@@ -54,7 +54,7 @@ void cx18_enqueue(struct cx18_stream *s, struct cx18_buffer *buf,
         }
         spin_lock_irqsave(&s->qlock, flags);
         list_add_tail(&buf->list, &q->list);
-        q->buffers++;
+        atomic_inc(&q->buffers);
         q->bytesused += buf->bytesused - buf->readpos;
         spin_unlock_irqrestore(&s->qlock, flags);
 }
@@ -68,7 +68,7 @@ struct cx18_buffer *cx18_dequeue(struct cx18_stream *s, struct cx18_queue *q)
         if (!list_empty(&q->list)) {
                 buf = list_entry(q->list.next, struct cx18_buffer, list);
                 list_del_init(q->list.next);
-                q->buffers--;
+                atomic_dec(&q->buffers);
                 q->bytesused -= buf->bytesused - buf->readpos;
         }
         spin_unlock_irqrestore(&s->qlock, flags);
@@ -92,8 +92,8 @@ struct cx18_buffer *cx18_queue_get_buf_irq(struct cx18_stream *s, u32 id,
                 /* the transport buffers are handled differently,
                    they are not moved to the full queue */
                 if (s->type != CX18_ENC_STREAM_TYPE_TS) {
-                        s->q_free.buffers--;
-                        s->q_full.buffers++;
+                        atomic_dec(&s->q_free.buffers);
+                        atomic_inc(&s->q_full.buffers);
                         s->q_full.bytesused += buf->bytesused;
                         list_move_tail(&buf->list, &s->q_full.list);
                 }
@@ -119,7 +119,7 @@ static void cx18_queue_flush(struct cx18_stream *s, struct cx18_queue *q)
                 buf = list_entry(q->list.next, struct cx18_buffer, list);
                 list_move_tail(q->list.next, &s->q_free.list);
                 buf->bytesused = buf->readpos = buf->b_flags = 0;
-                s->q_free.buffers++;
+                atomic_inc(&s->q_free.buffers);
         }
         cx18_queue_init(q);
         spin_unlock_irqrestore(&s->qlock, flags);