diff options
Diffstat (limited to 'block/ll_rw_blk.c')
| -rw-r--r-- | block/ll_rw_blk.c | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c index 3d0422f48453..768987dc2697 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); |