[PATCH v2 4/5] block: Reduce the minimum value for the maximum DMA segment size

[Bart Van Assche <bvanassche@acm.org>]

All block devices that are supported by the Linux kernel have a DMA engine
that supports DMA segments of 4 KiB or larger. Allow smaller DMA segment
sizes because these are useful for block layer testing. Reject values below
512 because such values would result in an excessive number of DMA segments.

The only code affected by this change is the following code:

	if (WARN_ON_ONCE(lim->max_segment_size < BLK_MIN_SEGMENT_SIZE))
		return -EINVAL;

Cc: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk.h b/block/blk.h
index 7082dd5a87f9..7c792c012b0d 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -23,7 +23,7 @@ struct elv_change_ctx;
 #define BLK_DEF_MAX_SECTORS_CAP	(SZ_4M >> SECTOR_SHIFT)
 
 #define	BLK_DEV_MAX_SECTORS	(LLONG_MAX >> 9)
-#define	BLK_MIN_SEGMENT_SIZE	4096
+#define	BLK_MIN_SEGMENT_SIZE	512
 
 /* Max future timer expiry for timeouts */
 #define BLK_MAX_TIMEOUT		(5 * HZ)