From 28e1ff70a08d331703f115534bd4278e11451439 Mon Sep 17 00:00:00 2001 From: Ricardo Ribalda Date: Wed, 21 Dec 2022 20:34:51 +0100 Subject: [PATCH] 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 Reviewed-by: Laurent Pinchart Signed-off-by: Ricardo Ribalda Acked-by: Alan Stern Link: https://lore.kernel.org/r/20221220-usb-dmadoc-v4-0-74a045bf14f4@chromium.org Signed-off-by: Greg Kroah-Hartman --- include/linux/usb.h | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff --git a/include/linux/usb.h b/include/linux/usb.h index 7d5325d47c451..4e98ebacec96b 100644 --- a/include/linux/usb.h +++ b/include/linux/usb.h @@ -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 -- 2.30.2