[media] davinci: vpif_capture: fix start/stop streaming locking

Video capture subdevs may be over I2C and may sleep during xfer, so we
cannot do IRQ-disabled locking when calling the subdev.

The IRQ-disabled locking is meant to protect the DMA queue list
throughout the rest of the driver, so update the locking in
[start|stop]_streaming to protect just this list, and update the irqlock
comment to reflect what it actually protects.

Suggested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/platform/davinci/vpif_capture.c

@@ -175,8 +175,6 @@ static int vpif_start_streaming(struct vb2_queue *vq, unsigned int count)
 	unsigned long addr, flags;
 	int ret;
 
-	spin_lock_irqsave(&common->irqlock, flags);
-
 	/* Initialize field_id */
 	ch->field_id = 0;
 
@@ -207,6 +205,7 @@ static int vpif_start_streaming(struct vb2_queue *vq, unsigned int count)
 	vpif_config_addr(ch, ret);
 
 	/* Get the next frame from the buffer queue */
+	spin_lock_irqsave(&common->irqlock, flags);
 	common->cur_frm = common->next_frm = list_entry(common->dma_queue.next,
 				    struct vpif_cap_buffer, list);
 	/* Remove buffer from the buffer queue */
@@ -240,6 +239,7 @@ static int vpif_start_streaming(struct vb2_queue *vq, unsigned int count)
 	return 0;
 
 err:
+	spin_lock_irqsave(&common->irqlock, flags);
 	list_for_each_entry_safe(buf, tmp, &common->dma_queue, list) {
 		list_del(&buf->list);
 		vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_QUEUED);
@@ -283,7 +283,6 @@ static void vpif_stop_streaming(struct vb2_queue *vq)
 		vpif_dbg(1, debug, "stream off failed in subdev\n");
 
 	/* release all active buffers */
-	spin_lock_irqsave(&common->irqlock, flags);
 	if (common->cur_frm == common->next_frm) {
 		vb2_buffer_done(&common->cur_frm->vb.vb2_buf,
 				VB2_BUF_STATE_ERROR);
@@ -296,6 +295,7 @@ static void vpif_stop_streaming(struct vb2_queue *vq)
 					VB2_BUF_STATE_ERROR);
 	}
 
+	spin_lock_irqsave(&common->irqlock, flags);
 	while (!list_empty(&common->dma_queue)) {
 		common->next_frm = list_entry(common->dma_queue.next,
 						struct vpif_cap_buffer, list);

drivers/media/platform/davinci/vpif_capture.h

@@ -63,7 +63,7 @@ struct common_obj {
 	struct vb2_queue buffer_queue;
 	/* Queue of filled frames */
 	struct list_head dma_queue;
-	/* Used in video-buf */
+	/* Protects the dma_queue field */
 	spinlock_t irqlock;
 	/* lock used to access this structure */
 	struct mutex lock;