firewire: Add a comment to describe why we split the sg list.
Signed-off-by: Kristian Hoegsberg <krh@redhat.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/fw-sbp2.c b/drivers/firewire/fw-sbp2.c
index 07be24e..cb808d5 100644
--- a/drivers/firewire/fw-sbp2.c
+++ b/drivers/firewire/fw-sbp2.c
@@ -926,7 +926,10 @@
/*
* Convert the scatterlist to an sbp2 page table. If any
- * scatterlist entries are too big for sbp2 we split the as we go.
+ * scatterlist entries are too big for sbp2, we split them as we
+ * go. Even if we ask the block I/O layer to not give us sg
+ * elements larger than 65535 bytes, some IOMMUs may merge sg elements
+ * during DMA mapping, and Linux currently doesn't prevent this.
*/
for (i = 0, j = 0; i < count; i++) {
sg_len = sg_dma_len(sg + i);