dma-mapping: factor out dummy DMA ops

The dummy DMA ops are currently used by arm64 for any device which has
an invalid ACPI description and is thus barred from using DMA due to not
knowing whether is is cache-coherent or not. Factor these out into
general dma-mapping code so that they can be referenced from other
common code paths. In the process, we can prune all the optional
callbacks which just do the same thing as the default behaviour, and
fill in .map_resource for completeness.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
[hch: moved to a separate source file]
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

2 files changed, 40 insertions, 1 deletions

diff --git a/kernel/dma/Makefile b/kernel/dma/Makefile
index a626f643cd63..72ff6e46aa86 100644
--- a/kernel/dma/Makefile
+++ b/kernel/dma/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_HAS_DMA)			+= mapping.o direct.o
+obj-$(CONFIG_HAS_DMA)			+= mapping.o direct.o dummy.o
 obj-$(CONFIG_DMA_CMA)			+= contiguous.o
 obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += coherent.o
 obj-$(CONFIG_DMA_VIRT_OPS)		+= virt.o
diff --git a/kernel/dma/dummy.c b/kernel/dma/dummy.c
new file mode 100644
index 000000000000..05607642c888
--- /dev/null
+++ b/kernel/dma/dummy.c
@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Dummy DMA ops that always fail.
+ */
+#include <linux/dma-mapping.h>
+
+static int dma_dummy_mmap(struct device *dev, struct vm_area_struct *vma,
+		void *cpu_addr, dma_addr_t dma_addr, size_t size,
+		unsigned long attrs)
+{
+	return -ENXIO;
+}
+
+static dma_addr_t dma_dummy_map_page(struct device *dev, struct page *page,
+		unsigned long offset, size_t size, enum dma_data_direction dir,
+		unsigned long attrs)
+{
+	return DMA_MAPPING_ERROR;
+}
+
+static int dma_dummy_map_sg(struct device *dev, struct scatterlist *sgl,
+		int nelems, enum dma_data_direction dir,
+		unsigned long attrs)
+{
+	return 0;
+}
+
+static int dma_dummy_supported(struct device *hwdev, u64 mask)
+{
+	return 0;
+}
+
+const struct dma_map_ops dma_dummy_ops = {
+	.mmap                   = dma_dummy_mmap,
+	.map_page               = dma_dummy_map_page,
+	.map_sg                 = dma_dummy_map_sg,
+	.dma_supported          = dma_dummy_supported,
+};
+EXPORT_SYMBOL(dma_dummy_ops);