[POWERPC] Fix initialization and usage of dma_mask

powerpc has a couple of bugs in the usage of dma_masks that tend to
break when drivers explicitly try to set a 32-bit mask for example.

First, the code that generates the pci devices from the OF device-tree
doesn't initialize the mask properly, then our implementation of
set_dma_mask() was trying to validate the -previous- mask value, not the
one passed in as an argument.

This fixes these problems.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/pci_64.c

@@ -313,6 +313,7 @@ struct pci_dev *of_create_pci_dev(struct device_node *node,
 
 	dev->current_state = 4;		/* unknown power state */
 	dev->error_state = pci_channel_io_normal;
+	dev->dma_mask = 0xffffffff;
 
 	if (!strcmp(type, "pci") || !strcmp(type, "pciex")) {
 		/* a PCI-PCI bridge */

include/asm-powerpc/dma-mapping.h

@@ -95,7 +95,7 @@ static inline int dma_set_mask(struct device *dev, u64 dma_mask)
 		return -EIO;
 	if (dma_ops->set_dma_mask != NULL)
 		return dma_ops->set_dma_mask(dev, dma_mask);
-	if (!dev->dma_mask || !dma_supported(dev, *dev->dma_mask))
+	if (!dev->dma_mask || !dma_supported(dev, dma_mask))
 		return -EIO;
 	*dev->dma_mask = dma_mask;
 	return 0;