On 10/01/18 08:00, Christoph Hellwig wrote:
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
include/linux/dma-direct.h | 1 +
lib/dma-direct.c | 19 +++++++++++++++++++
2 files changed, 20 insertions(+)
diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index 4788bf0bf683..bcdb1a3e4b1f 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -42,5 +42,6 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
gfp_t gfp, unsigned long attrs);
void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
dma_addr_t dma_addr, unsigned long attrs);
+int dma_direct_supported(struct device *dev, u64 mask);
#endif /* _LINUX_DMA_DIRECT_H */
diff --git a/lib/dma-direct.c b/lib/dma-direct.c
index 784a68dfdbe3..40b1f92f2214 100644
--- a/lib/dma-direct.c
+++ b/lib/dma-direct.c
@@ -122,6 +122,24 @@ static int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl,
return nents;
}
+int dma_direct_supported(struct device *dev, u64 mask)
+{
+#ifdef CONFIG_ZONE_DMA
+ if (mask < DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
+ return 0;
+#else
+ /*
+ * Because 32-bit DMA masks are so common we expect every architecture
+ * to be able to satisfy them - either by not supporting more physical
+ * memory, or by providing a ZONE_DMA32. If neither is the case, the
+ * architecture needs to use an IOMMU instead of the direct mapping.
+ */
+ if (mask < DMA_BIT_MASK(32))
+ return 0;
Do you think it's worth the effort to be a little more accommodating
here? i.e.:
return dma_max_pfn(dev) >= max_pfn;
We seem to have a fair few 28-31 bit masks for older hardware which
probably associates with host systems packing equivalently small amounts
of RAM.
Otherwise though,
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
Robin.
+#endif
+ return 1;
+}
+
static int dma_direct_mapping_error(struct device *dev, dma_addr_t dma_addr)
{
return dma_addr == DIRECT_MAPPING_ERROR;
@@ -132,6 +150,7 @@ const struct dma_map_ops dma_direct_ops = {
.free = dma_direct_free,
.map_page = dma_direct_map_page,
.map_sg = dma_direct_map_sg,
+ .dma_supported = dma_direct_supported,
.mapping_error = dma_direct_mapping_error,
};
EXPORT_SYMBOL(dma_direct_ops);
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