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.TH "USB_BUFFER_ALLOC" "9" "09 October 2005" "" ""

.SH NAME
usb_buffer_alloc \- allocate dma-consistent buffer for URB_NO_xxx_DMA_MAP
.SH SYNOPSIS
"SYNOPSIS"
.sp
\fB
.sp
void * usb_buffer_alloc  (struct usb_device * \fIdev\fB, size_t \fIsize\fB, unsigned \fImem_flags\fB, dma_addr_t * \fIdma\fB);
\fR
.SH "ARGUMENTS"
.TP
\fB\fIdev\fB\fR
device the buffer will be used with
.TP
\fB\fIsize\fB\fR
requested buffer size
.TP
\fB\fImem_flags\fB\fR
affect whether allocation may block
.TP
\fB\fIdma\fB\fR
used to return DMA address of buffer
.SH "DESCRIPTION"
.PP
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).
.PP
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.
.PP
When the buffer is no longer used, free it with \fBusb_buffer_free\fR\&.