NAME

ddi_dma_getwin - activate a new DMA window

SYNOPSIS

#include <sys/ddi.h>
#include <sys/sunddi.h>
int ddi_dma_getwin(ddi_dma_handle_t handle, uint_t win,
     off_t *offp, size_t *lenp, ddi_dma_cookie_t *cookiep,
     uint_t *ccountp);

INTERFACE LEVEL

illumos DDI specific (illumos DDI).

PARAMETERS

handle

The DMA handle previously allocated by a call to ddi_dma_alloc_handle(9F).

win

Number of the window to activate.

offp

Pointer to an offset. Upon a successful return, offp will contain the new offset indicating the beginning of the window within the object.

lenp

Upon a successful return, lenp will contain the size, in bytes, of the current window.

cookiep

A pointer to the first ddi_dma_cookie(9S) structure. This should be left as NULL in new callers.

ccountp

Upon a successful return, ccountp will contain the number of cookies for this DMA window. This can be left as NULL in new callers. The cookie count can be obtained by calling ddi_dma_ncookies(9F).

DESCRIPTION

ddi_dma_getwin() activates a new DMA window. If a DMA resource allocation request returns DDI_DMA_PARTIAL_MAP indicating that resources for less than the entire object were allocated, the current DMA window can be changed by a call to ddi_dma_getwin().

The caller must first determine the number of DMA windows, N, using ddi_dma_numwin(9F). ddi_dma_getwin() takes a DMA window number from the range [0..N-1] as the parameter win and makes it the current DMA window.

ddi_dma_getwin() allocates and assosciates a number of DMA cookies with handle. To get the total number of cookies, callers should use the ddi_dma_ncookies(9F) function. To get all of the cookies, callers should use the ddi_dma_cookie_iter(9F) or ddi_dma_cookie_get(9F) functions. Callers should pass NULL for cookiep and ccountp. These values are required if using the deprecated ddi_dma_nextcookie(9F) interface, in which case cookiep is filled in with the first ddi_dma_cookie(9S) structure.

ddi_dma_getwin() takes care of underlying resource synchronizations required to shift the window. However accessing the data prior to or after moving the window requires further synchronization steps using ddi_dma_sync(9F).

ddi_dma_getwin() is normally called from an interrupt routine. The first invocation of the DMA engine is done from the driver. All subsequent invocations of the DMA engine are done from the interrupt routine. The interrupt routine checks to see if the request has been completed. If it has, the interrupt routine returns without invoking another DMA transfer. Otherwise, it calls ddi_dma_getwin() to shift the current window and start another DMA transfer.

RETURN VALUES

ddi_dma_getwin() returns:

DDI_SUCCESS

Resources for the specified DMA window are allocated.

DDI_FAILURE

win is not a valid window index.

CONTEXT

ddi_dma_getwin() can be called from user, kernel, or interrupt context.