drm/vmwgfx: Use the dma scatter-gather iterator to get dma addresses

Use struct sg_dma_page_iter in favour struct of sg_page_iter, which fairly
recently was declared useless for obtaining dma addresses.

With a struct sg_dma_page_iter we can't call sg_page_iter_page() so
when the page is needed, use the same page lookup mechanism as for the
non-sg dma modes instead of calling sg_dma_page_iter.

Note, the fixes tag doesn't really point to a commit introducing a
failure / regression, but rather to a commit that implemented a simple
workaround for this problem.

Cc: Jason Gunthorpe <jgg@mellanox.com>
Fixes: d901b276 ("lib/scatterlist: Provide a DMA page iterator")
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/gpu/drm/vmwgfx/vmwgfx_drv.h

@@ -296,7 +296,7 @@ struct vmw_sg_table {
 struct vmw_piter {
 	struct page **pages;
 	const dma_addr_t *addrs;
-	struct sg_page_iter iter;
+	struct sg_dma_page_iter iter;
 	unsigned long i;
 	unsigned long num_pages;
 	bool (*next)(struct vmw_piter *);

drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c

@@ -266,7 +266,9 @@ static bool __vmw_piter_non_sg_next(struct vmw_piter *viter)
 
 static bool __vmw_piter_sg_next(struct vmw_piter *viter)
 {
-	return __sg_page_iter_next(&viter->iter);
+	bool ret = __vmw_piter_non_sg_next(viter);
+
+	return __sg_page_iter_dma_next(&viter->iter) && ret;
 }
 
 
@@ -284,12 +286,6 @@ static struct page *__vmw_piter_non_sg_page(struct vmw_piter *viter)
 	return viter->pages[viter->i];
 }
 
-static struct page *__vmw_piter_sg_page(struct vmw_piter *viter)
-{
-	return sg_page_iter_page(&viter->iter);
-}
-
-
 /**
  * Helper functions to return the DMA address of the current page.
  *
@@ -311,13 +307,7 @@ static dma_addr_t __vmw_piter_dma_addr(struct vmw_piter *viter)
 
 static dma_addr_t __vmw_piter_sg_addr(struct vmw_piter *viter)
 {
-	/*
-	 * FIXME: This driver wrongly mixes DMA and CPU SG list iteration and
-	 * needs revision. See
-	 * https://lore.kernel.org/lkml/20190104223531.GA1705@ziepe.ca/
-	 */
-	return sg_page_iter_dma_address(
-		container_of(&viter->iter, struct sg_dma_page_iter, base));
+	return sg_page_iter_dma_address(&viter->iter);
 }
 
 
@@ -336,26 +326,23 @@ void vmw_piter_start(struct vmw_piter *viter, const struct vmw_sg_table *vsgt,
 {
 	viter->i = p_offset - 1;
 	viter->num_pages = vsgt->num_pages;
+	viter->page = &__vmw_piter_non_sg_page;
+	viter->pages = vsgt->pages;
 	switch (vsgt->mode) {
 	case vmw_dma_phys:
 		viter->next = &__vmw_piter_non_sg_next;
 		viter->dma_address = &__vmw_piter_phys_addr;
-		viter->page = &__vmw_piter_non_sg_page;
-		viter->pages = vsgt->pages;
 		break;
 	case vmw_dma_alloc_coherent:
 		viter->next = &__vmw_piter_non_sg_next;
 		viter->dma_address = &__vmw_piter_dma_addr;
-		viter->page = &__vmw_piter_non_sg_page;
 		viter->addrs = vsgt->addrs;
-		viter->pages = vsgt->pages;
 		break;
 	case vmw_dma_map_populate:
 	case vmw_dma_map_bind:
 		viter->next = &__vmw_piter_sg_next;
 		viter->dma_address = &__vmw_piter_sg_addr;
-		viter->page = &__vmw_piter_sg_page;
-		__sg_page_iter_start(&viter->iter, vsgt->sgt->sgl,
+		__sg_page_iter_start(&viter->iter.base, vsgt->sgt->sgl,
 				     vsgt->sgt->orig_nents, p_offset);
 		break;
 	default: