[PATCH 2/5 v2] powerpc/dma-mapping: override dma_get_page_shift

Nishanth Aravamudan nacc at linux.vnet.ibm.com
Fri Oct 2 13:16:47 PDT 2015

On Power, the kernel's page size can differ from the IOMMU's page size,
so we need to override the generic implementation, which always returns
the kernel's page size. Lookup the IOMMU's page size from struct
iommu_table, if available. Fallback to the kernel's page size,

Signed-off-by: Nishanth Aravamudan <nacc at linux.vnet.ibm.com>

diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h
index 7f522c0..c5638f4 100644
--- a/arch/powerpc/include/asm/dma-mapping.h
+++ b/arch/powerpc/include/asm/dma-mapping.h
@@ -125,6 +125,9 @@ static inline void set_dma_offset(struct device *dev, dma_addr_t off)
 extern int dma_set_mask(struct device *dev, u64 dma_mask);
+extern unsigned long dma_get_page_shift(struct device *dev);
 #include <asm-generic/dma-mapping-common.h>
 extern int __dma_set_mask(struct device *dev, u64 dma_mask);
diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
index 59503ed..e805af2 100644
--- a/arch/powerpc/kernel/dma.c
+++ b/arch/powerpc/kernel/dma.c
@@ -335,6 +335,15 @@ int dma_set_mask(struct device *dev, u64 dma_mask)
+unsigned long dma_get_page_shift(struct device *dev)
+	struct iommu_table *tbl = get_iommu_table_base(dev);
+	if (tbl)
+		return tbl->it_page_shift;
+	return PAGE_SHIFT;
 u64 __dma_get_required_mask(struct device *dev)
 	struct dma_map_ops *dma_ops = get_dma_ops(dev);

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