Commit 28e1ff70 authored by Ricardo Ribalda's avatar Ricardo Ribalda Committed by Greg Kroah-Hartman
Browse files

USB: Improve usb_fill_* documentation 



Document the transfer buffer requirement. That is, the buffer must be
DMAble - otherwise data corruption might occur.

Acked-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Reviewed-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: default avatarRicardo Ribalda <ribalda@chromium.org>
Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20221220-usb-dmadoc-v4-0-74a045bf14f4@chromium.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2582d629

include/linux/usb.h

+23 −4
Original line number Diff line number Diff line
@@ -1626,14 +1626,25 @@ struct urb { 
 * @urb: pointer to the urb to initialize.

 * @dev: pointer to the struct usb_device for this urb.

 * @pipe: the endpoint pipe

 * @setup_packet: pointer to the setup_packet buffer

 * @transfer_buffer: pointer to the transfer buffer

 * @setup_packet: pointer to the setup_packet buffer. The buffer must be

 *	suitable for DMA.

 * @transfer_buffer: pointer to the transfer buffer. The buffer must be

 *	suitable for DMA.

 * @buffer_length: length of the transfer buffer

 * @complete_fn: pointer to the usb_complete_t function

 * @context: what to set the urb context to.

 *

 * Initializes a control urb with the proper information needed to submit

 * it to a device.

 *

 * The transfer buffer and the setup_packet buffer will most likely be filled

 * or read via DMA. The simplest way to get a buffer that can be DMAed to is

 * allocating it via kmalloc() or equivalent, even for very small buffers.

 * If the buffers are embedded in a bigger structure, there is a risk that

 * the buffer itself, the previous fields and/or the next fields are corrupted

 * due to cache incoherencies; or slowed down if they are evicted from the

 * cache. For more information, check &struct urb.

 *

 */

static inline void usb_fill_control_urb(struct urb *urb,

					struct usb_device *dev,
@@ -1658,13 +1669,17 @@ static inline void usb_fill_control_urb(struct urb *urb, 
 * @urb: pointer to the urb to initialize.

 * @dev: pointer to the struct usb_device for this urb.

 * @pipe: the endpoint pipe

 * @transfer_buffer: pointer to the transfer buffer

 * @transfer_buffer: pointer to the transfer buffer. The buffer must be

 *	suitable for DMA.

 * @buffer_length: length of the transfer buffer

 * @complete_fn: pointer to the usb_complete_t function

 * @context: what to set the urb context to.

 *

 * Initializes a bulk urb with the proper information needed to submit it

 * to a device.

 *

 * Refer to usb_fill_control_urb() for a description of the requirements for

 * transfer_buffer.

 */

static inline void usb_fill_bulk_urb(struct urb *urb,

				     struct usb_device *dev,
@@ -1687,7 +1702,8 @@ static inline void usb_fill_bulk_urb(struct urb *urb, 
 * @urb: pointer to the urb to initialize.

 * @dev: pointer to the struct usb_device for this urb.

 * @pipe: the endpoint pipe

 * @transfer_buffer: pointer to the transfer buffer

 * @transfer_buffer: pointer to the transfer buffer. The buffer must be

 *	suitable for DMA.

 * @buffer_length: length of the transfer buffer

 * @complete_fn: pointer to the usb_complete_t function

 * @context: what to set the urb context to.
@@ -1697,6 +1713,9 @@ static inline void usb_fill_bulk_urb(struct urb *urb, 
 * Initializes a interrupt urb with the proper information needed to submit

 * it to a device.

 *

 * Refer to usb_fill_control_urb() for a description of the requirements for

 * transfer_buffer.

 *

 * Note that High Speed and SuperSpeed(+) interrupt endpoints use a logarithmic

 * encoding of the endpoint interval, and express polling intervals in

 * microframes (eight per millisecond) rather than in frames (one per