This way an architecture with less than 4G of RAM can support dma_mask
smaller than 32-bit without a ZONE_DMA. Apparently that is a common
case on powerpc.
Signed-off-by: Christoph Hellwig <h...@lst.de>
---
kernel/dma/direct.c | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 64466b7ef67b..d1e103c6b107 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -4,6 +4,7 @@
*
* DMA operations that map physical memory directly without using an IOMMU.
*/
+#include <linux/bootmem.h> /* for max_pfn */
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/dma-direct.h>
@@ -283,21 +284,24 @@ int dma_direct_map_sg(struct device *dev, struct
scatterlist *sgl, int nents,
return nents;
}
+/*
+ * 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.
+ */
int dma_direct_supported(struct device *dev, u64 mask)
{
-#ifdef CONFIG_ZONE_DMA
- if (mask < phys_to_dma(dev, 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 < phys_to_dma(dev, DMA_BIT_MASK(32)))
+ u64 min_mask;
+
+ if (IS_ENABLED(CONFIG_ZONE_DMA))
+ min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
+ else
+ min_mask = min_t(u64, DMA_BIT_MASK(32),
+ (max_pfn - 1) << PAGE_SHIFT);
+
+ if (mask >= phys_to_dma(dev, min_mask))
return 0;
-#endif
return 1;
}
--
2.18.0
