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blk_queue_dma_drain(9) [centos 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 3.10 June 2014 BLK_QUEUE_DMA_DRAIN(9)

Check Out this Related Man Page

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)
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