dma-mapping: Generalise dma_32bit_limit flag

Whilst the notion of an upstream DMA restriction is most commonly seen
in PCI host bridges saddled with a 32-bit native interface, a more
general version of the same issue can exist on complex SoCs where a bus
or point-to-point interconnect link from a device's DMA master interface
to another component along the path to memory (often an IOMMU) may carry
fewer address bits than the interfaces at both ends nominally support.
In order to properly deal with this, the first step is to expand the
dma_32bit_limit flag into an arbitrary mask.

To minimise the impact on existing code, we'll make sure to only
consider this new mask valid if set. That makes sense anyway, since a
mask of zero would represent DMA not being wired up at all, and that
would be better handled by not providing valid ops in the first place.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 3 insertions, 3 deletions

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8be8106270c2..c2860c5a9e96 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -180,10 +180,10 @@ int dma_direct_supported(struct device *dev, u64 mask)
 		return 0;
 #endif
 	/*
-	 * Various PCI/PCIe bridges have broken support for > 32bit DMA even
-	 * if the device itself might support it.
+	 * Upstream PCI/PCIe bridges or SoC interconnects may not carry
+	 * as many DMA address bits as the device itself supports.
 	 */
-	if (dev->dma_32bit_limit && mask > DMA_BIT_MASK(32))
+	if (dev->bus_dma_mask && mask > dev->bus_dma_mask)
 		return 0;
 	return 1;
 }