Merge git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6

* git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6: (142 commits)
  USB: Fix sysfs paths in documentation
  USB: skeleton: fix coding style issues.
  USB: O_NONBLOCK in read path of skeleton
  USB: make usb-skeleton honor O_NONBLOCK in write path
  USB: skel_read really sucks royally
  USB: Add hub descriptor update hook for xHCI
  USB: xhci: Support USB hubs.
  USB: xhci: Set multi-TT field for LS/FS devices under hubs.
  USB: xhci: Set route string for all devices.
  USB: xhci: Fix command wait list handling.
  USB: xhci: Change how xHCI commands are handled.
  USB: xhci: Refactor input device context setup.
  USB: xhci: Endpoint representation refactoring.
  USB: gadget: ether needs to select CRC32
  USB: fix USBTMC get_capabilities success handling
  USB: fix missing error check in probing
  USB: usbfs: add USBDEVFS_URB_BULK_CONTINUATION flag
  USB: support for autosuspend in sierra while online
  USB: ehci-dbgp,ehci: Allow dbpg to work with suspend/resume
  USB: ehci-dbgp,documentation: Documentation updates for ehci-dbgp
  ...

1 files changed, 10 insertions, 22 deletions

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 9720e699f47..da718e84d58 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -459,35 +459,23 @@ int usb_sg_init(struct usb_sg_request *io, struct usb_device *dev,
 			io->urbs[i]->context = io;
 
 			/*
-			 * Some systems need to revert to PIO when DMA is
-			 * temporarily unavailable.  For their sakes, both
-			 * transfer_buffer and transfer_dma are set when
-			 * possible.  However this can only work on systems
-			 * without:
+			 * Some systems need to revert to PIO when DMA is temporarily
+			 * unavailable.  For their sakes, both transfer_buffer and
+			 * transfer_dma are set when possible.
 			 *
-			 *  - HIGHMEM, since DMA buffers located in high memory
-			 *    are not directly addressable by the CPU for PIO;
-			 *
-			 *  - IOMMU, since dma_map_sg() is allowed to use an
-			 *    IOMMU to make virtually discontiguous buffers be
-			 *    "dma-contiguous" so that PIO and DMA need diferent
-			 *    numbers of URBs.
-			 *
-			 * So when HIGHMEM or IOMMU are in use, transfer_buffer
-			 * is NULL to prevent stale pointers and to help spot
-			 * bugs.
+			 * Note that if IOMMU coalescing occurred, we cannot
+			 * trust sg_page anymore, so check if S/G list shrunk.
 			 */
+			if (io->nents == io->entries && !PageHighMem(sg_page(sg)))
+				io->urbs[i]->transfer_buffer = sg_virt(sg);
+			else
+				io->urbs[i]->transfer_buffer = NULL;
+
 			if (dma) {
 				io->urbs[i]->transfer_dma = sg_dma_address(sg);
 				len = sg_dma_len(sg);
-#if defined(CONFIG_HIGHMEM) || defined(CONFIG_GART_IOMMU)
-				io->urbs[i]->transfer_buffer = NULL;
-#else
-				io->urbs[i]->transfer_buffer = sg_virt(sg);
-#endif
 			} else {
 				/* hc may use _only_ transfer_buffer */
-				io->urbs[i]->transfer_buffer = sg_virt(sg);
 				len = sg->length;
 			}