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-rw-r--r--include/linux/usb.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 475cb75cc378..112a2d6e922f 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1044,7 +1044,9 @@ typedef void (*usb_complete_t)(struct urb *);
* @setup_dma: For control transfers with URB_NO_SETUP_DMA_MAP set, the
* device driver has provided this DMA address for the setup packet.
* The host controller driver should use this in preference to
- * setup_packet.
+ * setup_packet, but the HCD may chose to ignore the address if it must
+ * copy the setup packet into internal structures. Therefore, setup_packet
+ * must always point to a valid buffer.
* @start_frame: Returns the initial frame for isochronous transfers.
* @number_of_packets: Lists the number of ISO transfer buffers.
* @interval: Specifies the polling interval for interrupt or isochronous