ddi_dma_nextwin

- get next DMA window

Synopsis

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

int ddi_dma_nextwin(ddi_dma_handle_t handle, ddi_dma_win_t win, 
     ddi_dma_win_t *nwin);

Interface Level

This interface is obsolete. ddi_dma_getwin(9F) should be used instead.

Parameters

handle

A DMA handle.

win

The current DMA window or NULL.

nwin

A pointer to the next DMA window to be filled in. If win is NULL, a pointer to the first window within the object is returned.

Description

The ddi_dma_nextwin() function shifts the current DMA window win within the object referred to by handle to the next DMA window nwin. If the current window is NULL, the first window within the object is returned. A DMA window is a portion of a DMA object or might be the entire object. A DMA window has system resources allocated to it and is prepared to accept data transfers. Examples of system resources are DVMA mapping resources and intermediate transfer buffer resources.

All DMA objects require a window. If the DMA window represents the whole DMA object it has system resources allocated for the entire data transfer. However, if the system is unable to setup the entire DMA object due to system resource limitations, the driver writer may allow the system to allocate system resources for less than the entire DMA object. This can be accomplished by specifying the DDI_DMA_PARTIAL flag as a parameter to ddi_dma_buf_setup(9F) or ddi_dma_addr_setup(9F) or as part of a ddi_dma_req(9S) structure in a call to ddi_dma_setup(9F).

Only the window that has resources allocated is valid per object at any one time. The currently valid window is the one that was most recently returned from ddi_dma_nextwin(). Furthermore, because a call to ddi_dma_nextwin() will reallocate system resources to the new window, the previous window will become invalid. It is a severe error to call ddi_dma_nextwin() before any transfers into the current window are complete.

The ddi_dma_nextwin() function takes care of underlying memory synchronizations required to shift the window. However, if you want to access the data before or after moving the window, further synchronizations using ddi_dma_sync(9F) are required.

Return Values

The ddi_dma_nextwin() function returns:

DDI_SUCCESS

Successfully filled in the next window pointer.

DDI_DMA_DONE

There is no next window. The current window is the final window within the specified object.

DDI_DMA_STALE

win does not refer to the currently active window.

Context

The ddi_dma_nextwin() function can be called from user, interrupt, or kernel context.

Examples

For an example see ddi_dma_segtocookie(9F).

Attributes

See attributes(5) for a description of the following attributes:

See Also

attributes(5), ddi_dma_addr_setup(9F), ddi_dma_buf_setup(9F), ddi_dma_getwin(9F), ddi_dma_nextseg(9F), ddi_dma_segtocookie(9F), ddi_dma_sync(9F), ddi_dma_req(9S)

Writing Device Drivers