Provided by: linux-doc-2.6.15_2.6.15-23.39_all
usb_buffer_alloc - allocate dma-consistent buffer for
void * usb_buffer_alloc (struct usb_device * dev, size_t size,
gfp_t mem_flags, dma_addr_t * dma);
dev device the buffer will be used with
size requested buffer size
affect whether allocation may block
dma used to return DMA address of buffer
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 tying down I/O mapping hardware for long idle periods.
The implementation varies between platforms, depending on details of
how DMA will work to this device. Using these buffers also helps
prevent cacheline sharing problems on architectures where CPU caches
are not DMA-coherent.
When the buffer is no longer used, free it with usb_buffer_free.