[PATCH 02/19] dma-buf-map: Add helper to initialize second map

[Lucas De Marchi <lucas.demarchi@intel.com>]

When dma_buf_map struct is passed around, it's useful to be able to
initialize a second map that takes care of reading/writing to an offset
of the original map.

Add a helper that copies the struct and add the offset to the proper
address.

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
---
 include/linux/dma-buf-map.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h
index 65e927d9ce33..3514a859f628 100644
--- a/include/linux/dma-buf-map.h
+++ b/include/linux/dma-buf-map.h
@@ -131,6 +131,35 @@ struct dma_buf_map {
 		.is_iomem = false, \
 	}
 
+/**
+ * DMA_BUF_MAP_INIT_OFFSET - Initializes struct dma_buf_map from another dma_buf_map
+ * @map_:	The dma-buf mapping structure to copy from
+ * @offset:	Offset to add to the other mapping
+ *
+ * Initializes a new dma_buf_struct based on another. This is the equivalent of doing:
+ *
+ * .. code-block: c
+ *
+ *	dma_buf_map map = other_map;
+ *	dma_buf_map_incr(&map, &offset);
+ *
+ * Example usage:
+ *
+ * .. code-block: c
+ *
+ *	void foo(struct device *dev, struct dma_buf_map *base_map)
+ *	{
+ *		...
+ *		struct dma_buf_map = DMA_BUF_MAP_INIT_OFFSET(base_map, FIELD_OFFSET);
+ *		...
+ *	}
+ */
+#define DMA_BUF_MAP_INIT_OFFSET(map_, offset_)	(struct dma_buf_map)	\
+	{								\
+		.vaddr = (map_)->vaddr + (offset_),			\
+		.is_iomem = (map_)->is_iomem,				\
+	}
+
 /**
  * dma_buf_map_set_vaddr - Sets a dma-buf mapping structure to an address in system memory
  * @map:	The dma-buf mapping structure
-- 
2.35.0