lib/scatterlist: Provide a DMA page iterator

Commit 2db76d7c3c6d ("lib/scatterlist: sg_page_iter: support sg lists w/o
backing pages") introduced the sg_page_iter_dma_address() function without
providing a way to use it in the general case. If the sg_dma_len() is not
equal to the sg length callers cannot safely use the
for_each_sg_page/sg_page_iter_dma_address combination.

Resolve this API mistake by providing a DMA specific iterator,
for_each_sg_dma_page(), that uses the right length so
sg_page_iter_dma_address() works as expected with all sglists.

A new iterator type is introduced to provide compile-time safety against
wrongly mixing accessors and iterators.

Acked-by: Christoph Hellwig <hch@lst.de> (for scatterlist)
Acked-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com> (ipu3-cio2)
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 9ba349e775ef..739dc9fe2c55 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -625,6 +625,32 @@ bool __sg_page_iter_next(struct sg_page_iter *piter)
 }
 EXPORT_SYMBOL(__sg_page_iter_next);
 
+static int sg_dma_page_count(struct scatterlist *sg)
+{
+        return PAGE_ALIGN(sg->offset + sg_dma_len(sg)) >> PAGE_SHIFT;
+}
+
+bool __sg_page_iter_dma_next(struct sg_dma_page_iter *dma_iter)
+{
+        struct sg_page_iter *piter = &dma_iter->base;
+
+        if (!piter->__nents || !piter->sg)
+                return false;
+
+        piter->sg_pgoffset += piter->__pg_advance;
+        piter->__pg_advance = 1;
+
+        while (piter->sg_pgoffset >= sg_dma_page_count(piter->sg)) {
+                piter->sg_pgoffset -= sg_dma_page_count(piter->sg);
+                piter->sg = sg_next(piter->sg);
+                if (!--piter->__nents || !piter->sg)
+                        return false;
+        }
+
+        return true;
+}
+EXPORT_SYMBOL(__sg_page_iter_dma_next);
+
 /**
  * sg_miter_start - start mapping iteration over a sg list
  * @miter: sg mapping iter to be started