USB_ALLOC_COHERENT(9) USB Core APIs USB_ALLOC_COHERENT(9)NAMEusb_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
DESCRIPTION
Return value is 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).
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.
COPYRIGHTKernel Hackers Manual 3.11 November 2013 USB_ALLOC_COHERENT(9)
