USB_SG_INIT(9) USB Core APIs USB_SG_INIT(9)NAME
usb_sg_init - initializes scatterlist-based bulk/interrupt I/O request
int usb_sg_init(struct usb_sg_request * io, struct usb_device * dev, unsigned pipe, unsigned period, struct scatterlist * sg, int nents,
size_t length, gfp_t mem_flags);
request block being initialized. until usb_sg_wait returns, treat this as a pointer to an opaque block of memory,
the usb device that will send or receive the data
endpoint "pipe" used to transfer the data
polling rate for interrupt endpoints, in frames or (for high speed endpoints) microframes; ignored for bulk
how many entries in the scatterlist
how many bytes to send from the scatterlist, or zero to send every byte identified in the list.
SLAB_* flags affecting memory allocations in this call
This initializes a scatter/gather request, allocating resources such as I/O mappings and urb memory (except maybe memory used by USB
The request must be issued using usb_sg_wait, which waits for the I/O to complete (or to be canceled) and then cleans up all resources
allocated by usb_sg_init.
The request may be canceled with usb_sg_cancel, either before or after usb_sg_wait is called.
Zero for success, else a negative errno value.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 USB_SG_INIT(9)
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USB_BUFFER_MAP_SG(9) USB Core APIs USB_BUFFER_MAP_SG(9)NAME
usb_buffer_map_sg - create scatterlist DMA mapping(s) for an endpoint
int usb_buffer_map_sg(const struct usb_device * dev, int is_in, struct scatterlist * sg, int nents);
device to which the scatterlist will be mapped
mapping transfer direction
the scatterlist to map
the number of entries in the scatterlist
Either < 0 (indicating no buffers could be mapped), or the number of DMA mapping array entries in the scatterlist.
The caller is responsible for placing the resulting DMA addresses from the scatterlist into URB transfer buffer pointers, and for setting
the URB_NO_TRANSFER_DMA_MAP transfer flag in each of those URBs.
Top I/O rates come from queuing URBs, instead of waiting for each one to complete before starting the next I/O. This is particularly easy
to do with scatterlists. Just allocate and submit one URB for each DMA mapping entry returned, stopping on the first error or when all
succeed. Better yet, use the usb_sg_*() calls, which do that (and more) for you.
This call would normally be used when translating scatterlist requests, rather than usb_buffer_map, since on some hardware (with IOMMUs) it
may be able to coalesce mappings for improved I/O efficiency.
Reverse the effect of this call with usb_buffer_unmap_sg.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 USB_BUFFER_MAP_SG(9)
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