blk_queue_dma_drain(9) [suse man page]

BLK_QUEUE_DMA_DRAIN(9)						   Block Devices					    BLK_QUEUE_DMA_DRAIN(9)

NAME

       blk_queue_dma_drain - Set up a drain buffer for excess dma.

SYNOPSIS

       int blk_queue_dma_drain(struct request_queue * q, dma_drain_needed_fn * dma_drain_needed, void * buf, unsigned int size);

ARGUMENTS

       q
	   the request queue for the device

       dma_drain_needed
	   fn which returns non-zero if drain is necessary

       buf
	   physically contiguous buffer

       size
	   size of the buffer in bytes

DESCRIPTION

       Some devices have excess DMA problems and can't simply discard (or zero fill) the unwanted piece of the transfer. They have to have a real
       area of memory to transfer it into. The use case for this is ATAPI devices in DMA mode. If the packet command causes a transfer bigger than
       the transfer size some HBAs will lock up if there aren't DMA elements to contain the excess transfer. What this API does is adjust the
       queue so that the buf is always appended silently to the scatterlist.

NOTE

       This routine adjusts max_hw_segments to make room for appending the drain buffer. If you call blk_queue_max_segments after calling this
       routine, you must set the limit to one fewer than your device can support otherwise there won't be room for the drain buffer.

COPYRIGHT

Kernel Hackers Manual 2.6.					     July 2010						    BLK_QUEUE_DMA_DRAIN(9)

ddi_iomin(9F)						   Kernel Functions for Drivers 					     ddi_iomin(9F)

NAME

       ddi_iomin - find minimum alignment and transfer size for DMA

SYNOPSIS

       #include <sys/conf.h>
       #include <sys/ddi.h>
       #include <sys/sunddi.h>

       int ddi_iomin(dev_info_t *dip, int initial, int streaming);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI).

PARAMETERS

       dip	       A pointer to the device's dev_info structure.

       initial	       The  initial  minimum  DMA  transfer  size  in  bytes.  This  may be zero or an appropriate dlim_minxfer value for device's
		       ddi_dma_lim structure (see ddi_dma_lim_sparc(9S) or ddi_dma_lim_x86(9S)).  This value must be a power of two.

       streaming       This argument, if non-zero, indicates that the returned value should be modified to account  for  streaming  mode  accesses
		       (see ddi_dma_req(9S) for a discussion of streaming versus non-streaming access mode).

DESCRIPTION

       ddi_iomin(),  finds  out  the  minimum  DMA transfer size for the device pointed to by dip. This provides a mechanism by which a driver can
       determine the effects of underlying caches as well as intervening bus adapters on the granularity of a DMA transfer.

RETURN VALUES

       ddi_iomin() returns the minimum DMA transfer size for the calling device, or it returns zero,  which means that you cannot get  there  from
       here.

CONTEXT

       This function can be called from user or interrupt context.

SEE ALSO

       ddi_dma_devalign(9F), ddi_dma_setup(9F), ddi_dma_sync(9F), ddi_dma_lim_sparc(9S), ddi_dma_lim_x86(9S), ddi_dma_req(9S)

       Writing Device Drivers

SunOS 5.10							    1 Feb 1994							     ddi_iomin(9F)