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-rw-r--r--block/elevator.c26
-rw-r--r--block/ll_rw_blk.c49
-rw-r--r--include/linux/blkdev.h4
3 files changed, 78 insertions, 1 deletions
diff --git a/block/elevator.c b/block/elevator.c
index f9736fbdab0..8cd5775acd7 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -741,7 +741,21 @@ struct request *elv_next_request(struct request_queue *q)
q->boundary_rq = NULL;
}
- if ((rq->cmd_flags & REQ_DONTPREP) || !q->prep_rq_fn)
+ if (rq->cmd_flags & REQ_DONTPREP)
+ break;
+
+ if (q->dma_drain_size && rq->data_len) {
+ /*
+ * make sure space for the drain appears we
+ * know we can do this because max_hw_segments
+ * has been adjusted to be one fewer than the
+ * device can handle
+ */
+ rq->nr_phys_segments++;
+ rq->nr_hw_segments++;
+ }
+
+ if (!q->prep_rq_fn)
break;
ret = q->prep_rq_fn(q, rq);
@@ -754,6 +768,16 @@ struct request *elv_next_request(struct request_queue *q)
* avoid resource deadlock. REQ_STARTED will
* prevent other fs requests from passing this one.
*/
+ if (q->dma_drain_size && rq->data_len &&
+ !(rq->cmd_flags & REQ_DONTPREP)) {
+ /*
+ * remove the space for the drain we added
+ * so that we don't add it again
+ */
+ --rq->nr_phys_segments;
+ --rq->nr_hw_segments;
+ }
+
rq = NULL;
break;
} else if (ret == BLKPREP_KILL) {
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 3d0422f4845..768987dc269 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -726,6 +726,45 @@ void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
EXPORT_SYMBOL(blk_queue_stack_limits);
/**
+ * blk_queue_dma_drain - Set up a drain buffer for excess dma.
+ *
+ * @q: the request queue for the device
+ * @buf: physically contiguous buffer
+ * @size: size of the buffer in bytes
+ *
+ * Some devices have excess DMA problems and can't simply discard (or
+ * zero fill) the unwanted piece of the transfer. They have to have a
+ * real area of memory to transfer it into. The use case for this is
+ * ATAPI devices in DMA mode. If the packet command causes a transfer
+ * bigger than the transfer size some HBAs will lock up if there
+ * aren't DMA elements to contain the excess transfer. What this API
+ * does is adjust the queue so that the buf is always appended
+ * silently to the scatterlist.
+ *
+ * Note: This routine adjusts max_hw_segments to make room for
+ * appending the drain buffer. If you call
+ * blk_queue_max_hw_segments() or blk_queue_max_phys_segments() after
+ * calling this routine, you must set the limit to one fewer than your
+ * device can support otherwise there won't be room for the drain
+ * buffer.
+ */
+int blk_queue_dma_drain(struct request_queue *q, void *buf,
+ unsigned int size)
+{
+ if (q->max_hw_segments < 2 || q->max_phys_segments < 2)
+ return -EINVAL;
+ /* make room for appending the drain */
+ --q->max_hw_segments;
+ --q->max_phys_segments;
+ q->dma_drain_buffer = buf;
+ q->dma_drain_size = size;
+
+ return 0;
+}
+
+EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
+
+/**
* blk_queue_segment_boundary - set boundary rules for segment merging
* @q: the request queue for the device
* @mask: the memory boundary mask
@@ -1379,6 +1418,16 @@ new_segment:
bvprv = bvec;
} /* segments in rq */
+ if (q->dma_drain_size) {
+ sg->page_link &= ~0x02;
+ sg = sg_next(sg);
+ sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
+ q->dma_drain_size,
+ ((unsigned long)q->dma_drain_buffer) &
+ (PAGE_SIZE - 1));
+ nsegs++;
+ }
+
if (sg)
sg_mark_end(sg);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c7a3ab575c2..e542c8fd921 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -429,6 +429,8 @@ struct request_queue
unsigned int max_segment_size;
unsigned long seg_boundary_mask;
+ void *dma_drain_buffer;
+ unsigned int dma_drain_size;
unsigned int dma_alignment;
struct blk_queue_tag *queue_tags;
@@ -760,6 +762,8 @@ extern void blk_queue_max_hw_segments(struct request_queue *, unsigned short);
extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
extern void blk_queue_hardsect_size(struct request_queue *, unsigned short);
extern void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b);
+extern int blk_queue_dma_drain(struct request_queue *q, void *buf,
+ unsigned int size);
extern void blk_queue_segment_boundary(struct request_queue *, unsigned long);
extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn);
extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *);