[PATCHv6 11/11] iomap: add support for dma aligned direct-io

[Keith Busch]

On Wed, Jun 29, 2022 at 02:04:47PM -0400, Eric Farman wrote:
> s390 dasd
> 
> This made me think to change my rootfs, and of course the problem goes
> away once on something like a SCSI volume.
> 
> So crawling through the dasd (instead of virtio) driver and I finally
> find the point where a change to dma_alignment (which you mentioned
> earlier) would actually fit.
> 
> Such a change fixes this for me, so I'll run it by our DASD guys.
> Thanks for your help and patience.

I'm assuming there's some driver or device requirement that's making this
necessary. Is the below driver change what you're looking for? If so, I think
you might want this regardless of this direct-io patch just because other
interfaces like blk_rq_map_user_iov() and blk_rq_aligned() align to it.

---
diff --git a/drivers/s390/block/dasd_fba.c b/drivers/s390/block/dasd_fba.c
index 60be7f7bf2d1..5c79fb02cded 100644
--- a/drivers/s390/block/dasd_fba.c
+++ b/drivers/s390/block/dasd_fba.c
@@ -780,6 +780,7 @@ static void dasd_fba_setup_blk_queue(struct dasd_block *block)
 	/* With page sized segments each segment can be translated into one idaw/tidaw */
 	blk_queue_max_segment_size(q, PAGE_SIZE);
 	blk_queue_segment_boundary(q, PAGE_SIZE - 1);
+	blk_queue_dma_alignment(q, PAGE_SIZE - 1);
 
 	q->limits.discard_granularity = logical_block_size;
 
--