centos man page for usb_alloc_coherent

USB_ALLOC_COHERENT(9)						   USB Core APIs					     USB_ALLOC_COHERENT(9)

NAME
       usb_alloc_coherent - allocate dma-consistent buffer for URB_NO_xxx_DMA_MAP

SYNOPSIS
       void * usb_alloc_coherent(struct usb_device * dev, size_t size, gfp_t mem_flags, dma_addr_t * dma);

ARGUMENTS
       dev
	   device the buffer will be used with

       size
	   requested buffer size

       mem_flags
	   affect whether allocation may block

       dma
	   used to return DMA address of buffer

RETURN
       Either null (indicating no buffer could be allocated), or the cpu-space pointer to a buffer that may be used to perform DMA to the
       specified device. Such cpu-space buffers are returned along with the DMA address (through the pointer provided).

NOTE
       These buffers are used with URB_NO_xxx_DMA_MAP set in urb->transfer_flags to avoid behaviors like using "DMA bounce buffers", or thrashing
       IOMMU hardware during URB completion/resubmit. The implementation varies between platforms, depending on details of how DMA will work to
       this device. Using these buffers also eliminates cacheline sharing problems on architectures where CPU caches are not DMA-coherent. On
       systems without bus-snooping caches, these buffers are uncached.

       When the buffer is no longer used, free it with usb_free_coherent.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						     USB_ALLOC_COHERENT(9)