ioat: fix size of 'completion' for Xen

Starting with v3.2 Jonathan reports that Xen crashes loading the ioatdma
driver.  A debug run shows:

  ioatdma 0000:00:16.4: desc[0]: (0x300cc7000->0x300cc7040) cookie: 0 flags: 0x2 ctl: 0x29 (op: 0 int_en: 1 compl: 1)
  ...
  ioatdma 0000:00:16.4: ioat_get_current_completion: phys_complete: 0xcc7000

...which shows that in this environment GFP_KERNEL memory may be backed
by a 64-bit dma address.  This breaks the driver's assumption that an
unsigned long should be able to contain the physical address for
descriptor memory.  Switch to dma_addr_t which beyond being the right
size, is the true type for the data i.e. an io-virtual address
inidicating the engine's last processed descriptor.

[stable: 3.2+]
Cc: <stable@vger.kernel.org>
Reported-by: Jonathan Nieder <jrnieder@gmail.com>
Reported-by: William Dauchy <wdauchy@gmail.com>
Tested-by: William Dauchy <wdauchy@gmail.com>
Tested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/ioat/dma.h

@@ -88,7 +88,7 @@ struct ioatdma_device {
 struct ioat_chan_common {
 	struct dma_chan common;
 	void __iomem *reg_base;
-	unsigned long last_completion;
+	dma_addr_t last_completion;
 	spinlock_t cleanup_lock;
 	dma_cookie_t completed_cookie;
 	unsigned long state;
@@ -333,7 +333,7 @@ int __devinit ioat_dma_self_test(struct ioatdma_device *device);
 void __devexit ioat_dma_remove(struct ioatdma_device *device);
 struct dca_provider * __devinit ioat_dca_init(struct pci_dev *pdev,
 					      void __iomem *iobase);
-unsigned long ioat_get_current_completion(struct ioat_chan_common *chan);
+dma_addr_t ioat_get_current_completion(struct ioat_chan_common *chan);
 void ioat_init_channel(struct ioatdma_device *device,
 		       struct ioat_chan_common *chan, int idx);
 enum dma_status ioat_dma_tx_status(struct dma_chan *c, dma_cookie_t cookie,
@@ -341,7 +341,7 @@ enum dma_status ioat_dma_tx_status(struct dma_chan *c, dma_cookie_t cookie,
 void ioat_dma_unmap(struct ioat_chan_common *chan, enum dma_ctrl_flags flags,
 		    size_t len, struct ioat_dma_descriptor *hw);
 bool ioat_cleanup_preamble(struct ioat_chan_common *chan,
-			   unsigned long *phys_complete);
+			   dma_addr_t *phys_complete);
 void ioat_kobject_add(struct ioatdma_device *device, struct kobj_type *type);
 void ioat_kobject_del(struct ioatdma_device *device);
 extern const struct sysfs_ops ioat_sysfs_ops;