Hi Suravee,

On 05/05/15 16:12, Suravee Suthikulpanit wrote:

 From http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf,
section 6.2.17 _CCA states that ARM platforms require ACPI _CCA
object to be specified for DMA-cabpable devices. This patch introduces
ACPI_MUST_HAVE_CCA in arm64 Kconfig to specify such requirement.

In this case of missing _CCA, arm64 would assign dummy_dma_ops
to disable DMA capability of the device.

Signed-off-by: Mark Salter <redacted>
Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
---

[...]

+static void __dummy_sync_single_for_cpu(struct device *dev,
+					dma_addr_t dev_addr, size_t size,
+					enum dma_data_direction dir)
+{
+}
+
+static void __dummy_sync_single_for_device(struct device *dev,
+					   dma_addr_t dev_addr, size_t size,
+					   enum dma_data_direction dir)
+{
+}

Minor point, but I don't see the need to have multiple dummy functions 
with identical signatures - just have a generic dummy_sync_single and 
assign it to both ops.

+static void __dummy_sync_sg_for_cpu(struct device *dev,
+				    struct scatterlist *sgl, int nelems,
+				    enum dma_data_direction dir)
+{
+}
+
+static void __dummy_sync_sg_for_device(struct device *dev,
+				       struct scatterlist *sgl, int nelems,
+				       enum dma_data_direction dir)
+{
+}

Ditto here with dummy_sync_sg.

I wonder if there's any argument for putting the dummy DMA ops somewhere 
common, like drivers/base/dma-mapping.c?

Robin.