diff options
Diffstat (limited to 'include/linux/usb.h')
| -rw-r--r-- | include/linux/usb.h | 27 |
1 files changed, 23 insertions, 4 deletions
diff --git a/include/linux/usb.h b/include/linux/usb.h index 86d1c8e79566..9642ee02d713 100644 --- a/include/linux/usb.h +++ b/include/linux/usb.h @@ -1628,14 +1628,25 @@ 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, @@ -1660,13 +1671,17 @@ 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, @@ -1689,7 +1704,8 @@ 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. @@ -1699,6 +1715,9 @@ 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 |