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-rw-r--r--drivers/usb/core/message.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index da4ee07e0094..b7434787db5f 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -412,10 +412,24 @@ int usb_sg_init (
io->urbs [i]->status = -EINPROGRESS;
io->urbs [i]->actual_length = 0;
+ /*
+ * 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
+ * to prevent stale pointers and to help spot bugs.
+ */
if (dma) {
- /* hc may use _only_ transfer_dma */
io->urbs [i]->transfer_dma = sg_dma_address (sg + i);
len = sg_dma_len (sg + i);
+#ifdef CONFIG_HIGHMEM
+ io->urbs[i]->transfer_buffer = NULL;
+#else
+ io->urbs[i]->transfer_buffer =
+ page_address(sg[i].page) + sg[i].offset;
+#endif
} else {
/* hc may use _only_ transfer_buffer */
io->urbs [i]->transfer_buffer =