dma-mapping: introduce dma_get_merge_boundary()

This patch adds a new DMA API "dma_get_merge_boundary". This function
returns the DMA merge boundary if the DMA layer can merge the segments.
This patch also adds the implementation for a new dma_map_ops pointer.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Christoph Hellwig <hch@lst.de>

3 files changed, 25 insertions, 0 deletions

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index e47c63bd4887..9c4dd3d779ed 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -204,6 +204,14 @@ Returns the maximum size of a mapping for the device. The size parameter
 of the mapping functions like dma_map_single(), dma_map_page() and
 others should not be larger than the returned value.
 
+::
+
+        unsigned long
+        dma_get_merge_boundary(struct device *dev);
+
+Returns the DMA merge boundary. If the device cannot merge any the DMA address
+segments, the function returns 0.
+
 Part Id - Streaming DMA mappings
 --------------------------------
 
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 48ebe8295987..de41a4f0b9f6 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -131,6 +131,7 @@ struct dma_map_ops {
         int (*dma_supported)(struct device *dev, u64 mask);
         u64 (*get_required_mask)(struct device *dev);
         size_t (*max_mapping_size)(struct device *dev);
+        unsigned long (*get_merge_boundary)(struct device *dev);
 };
 
 #define DMA_MAPPING_ERROR               (~(dma_addr_t)0)
@@ -467,6 +468,7 @@ int dma_set_mask(struct device *dev, u64 mask);
 int dma_set_coherent_mask(struct device *dev, u64 mask);
 u64 dma_get_required_mask(struct device *dev);
 size_t dma_max_mapping_size(struct device *dev);
+unsigned long dma_get_merge_boundary(struct device *dev);
 #else /* CONFIG_HAS_DMA */
 static inline dma_addr_t dma_map_page_attrs(struct device *dev,
                 struct page *page, size_t offset, size_t size,
@@ -572,6 +574,10 @@ static inline size_t dma_max_mapping_size(struct device *dev)
 {
         return 0;
 }
+static inline unsigned long dma_get_merge_boundary(struct device *dev)
+{
+        return 0;
+}
 #endif /* CONFIG_HAS_DMA */
 
 static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 1b96616c9f20..72c825c1788e 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -407,3 +407,14 @@ size_t dma_max_mapping_size(struct device *dev)
         return size;
 }
 EXPORT_SYMBOL_GPL(dma_max_mapping_size);
+
+unsigned long dma_get_merge_boundary(struct device *dev)
+{
+        const struct dma_map_ops *ops = get_dma_ops(dev);
+
+        if (!ops || !ops->get_merge_boundary)
+                return 0;       /* can't merge */
+
+        return ops->get_merge_boundary(dev);
+}
+EXPORT_SYMBOL_GPL(dma_get_merge_boundary);