dma-mapping: add a dma_can_mmap helper

Add a helper to check if DMA allocations for a specific device can be
mapped to userspace using dma_mmap_*.

Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 23 insertions, 0 deletions

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index c8b4e46407ba..18ba1ac93fc1 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -223,6 +223,29 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
 }
 
 /**
+ * dma_can_mmap - check if a given device supports dma_mmap_*
+ * @dev: device to check
+ *
+ * Returns %true if @dev supports dma_mmap_coherent() and dma_mmap_attrs() to
+ * map DMA allocations to userspace.
+ */
+bool dma_can_mmap(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (IS_ENABLED(CONFIG_ARCH_NO_COHERENT_DMA_MMAP))
+		return false;
+
+	if (dma_is_direct(ops)) {
+		return dev_is_dma_coherent(dev) ||
+			IS_ENABLED(CONFIG_ARCH_HAS_DMA_COHERENT_TO_PFN);
+	}
+
+	return ops->mmap != NULL;
+}
+EXPORT_SYMBOL_GPL(dma_can_mmap);
+
+/**
  * dma_mmap_attrs - map a coherent DMA allocation into user space
  * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
  * @vma: vm_area_struct describing requested user mapping