From 13369891d8b5cdd78974b116ed1ce00bea870eea Mon Sep 17 00:00:00 2001
From: David Brownell <david-b@pacbell.net>
Date: Sun, 22 Jul 2007 15:13:13 -0700
Subject: [PATCH] --- yaml --- r: 63199 b: refs/heads/master c:
 a12b8db02035673153bbf19bb3641a08bed9e4b8 h: refs/heads/master i:   63197:
 abb34fdf626d0bec9b6019e484f917d51abc70ef   63195:
 573f8886a60fdc45f6518eab09f8688b0df69bed   63191:
 def0a819e1aa6dcfc1ec2169e59a729d39386076   63183:
 1f8ed2748b6ac7399076db13e121c4abe1808b4e   63167:
 a765c78e4799bfba6c6bde828ad57fe5e9436752 v: v3

---
 [refs]                           |  2 +-
 trunk/drivers/usb/core/message.c | 15 +++++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/[refs] b/[refs]
index ab568622aea6..024dba636334 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: e31c18804f584dd838a752f6628e8c15bd7a3372
+refs/heads/master: a12b8db02035673153bbf19bb3641a08bed9e4b8
diff --git a/trunk/drivers/usb/core/message.c b/trunk/drivers/usb/core/message.c
index 25f63f1096b4..ad4b956380d2 100644
--- a/trunk/drivers/usb/core/message.c
+++ b/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 =