---

yaml
---
r: 63199
b: refs/heads/master
c: a12b8db
h: refs/heads/master
i:
  63197: abb34fd
  63195: 573f888
  63191: def0a81
  63183: 1f8ed27
  63167: a765c78
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: e31c18804f584dd838a752f6628e8c15bd7a3372
+refs/heads/master: a12b8db02035673153bbf19bb3641a08bed9e4b8

trunk/drivers/usb/core/message.c

@@ -411,15 +411,22 @@ int usb_sg_init (
 		 * 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 HIGHMEM, since DMA buffers located
-		 * in high memory are not directly addressable by the CPU for
-		 * PIO ... so when HIGHMEM is in use, transfer_buffer is NULL
+		 * work on systems without:
+		 *
+		 *  - 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.
 		 */
 		if (dma) {
 			io->urbs [i]->transfer_dma = sg_dma_address (sg + i);
 			len = sg_dma_len (sg + i);
-#ifdef CONFIG_HIGHMEM
+#if defined(CONFIG_HIGHMEM) || defined(CONFIG_IOMMU)
 			io->urbs[i]->transfer_buffer = NULL;
 #else
 			io->urbs[i]->transfer_buffer =