dma-direct: always allow dma mask <= physiscal memory size

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 <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 60c433b..170bd32 100644 (file)
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -284,21 +284,25 @@ 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 = DMA_BIT_MASK(32);
+
+       min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
+
+       if (mask >= phys_to_dma(dev, min_mask))
                return 0;
-#endif
        return 1;
 }