KFIFO_DMA_OUT_PREPAR(9) FIFO Buffer KFIFO_DMA_OUT_PREPAR(9)NAME
kfifo_dma_out_prepare - setup a scatterlist for DMA output
kfifo_dma_out_prepare(fifo, sgl, nents, len);
address of the fifo to be used
pointer to the scatterlist array
number of entries in the scatterlist array
number of elements to transfer
This macro fills a scatterlist for DMA output which at most len bytes to transfer. It returns the number entries in the scatterlist array.
A zero means there is no space available and the scatterlist is not filled.
Note that with only one concurrent reader and one concurrent writer, you don't need extra locking to use these macros.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 KFIFO_DMA_OUT_PREPAR(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
Return value is 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 2.6. July 2010 USB_BUFFER_MAP_SG(9)
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