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USB: Improve usb_fill_* documentation 

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

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20221220-usb-dmadoc-v4-0-74a045bf14f4@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ricardo Ribalda 2022-12-21 20:34:51 +01:00 committed by Greg Kroah-Hartman
parent 2582d629c9
commit 28e1ff70a0
1 changed files with 23 additions and 4 deletions
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27
include/linux/usb.h
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@ -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