core, dma-direct: add a flag 32-bit dma limits

Various PCI bridges (VIA PCI, Xilinx PCIe) limit DMA to only 32-bits
even if the device itself supports more.  Add a single bit flag to
struct device (to be moved into the dma extension once we get to it)
to flag such devices and reject larger DMA to them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

lib/dma-direct.c

@@ -172,6 +172,12 @@ int dma_direct_supported(struct device *dev, u64 mask)
 	if (mask < DMA_BIT_MASK(32))
 		return 0;
 #endif
+	/*
+	 * Various PCI/PCIe bridges have broken support for > 32bit DMA even
+	 * if the device itself might support it.
+	 */
+	if (dev->dma_32bit_limit && mask > DMA_BIT_MASK(32))
+		return 0;
 	return 1;
 }