Solaris DDI specific (Solaris DDI).

win

A DMA window.

seg

The current DMA segment or NULL.

nseg

A pointer to the next DMA segment to be filled in. If seg is NULL, a pointer to the first segment within the specified window is returned.

ddi_dma_nextseg() gets the next DMA segment within the specified window win. If the current segment is NULL, the first DMA segment within the window is returned.

A DMA segment is always required for a DMA window. A DMA segment is a contiguous portion of a DMA window (see ddi_dma_nextwin(9F)) which is entirely addressable by the device for a data transfer operation.

An example where multiple DMA segments are allocated is where the system does not contain DVMA capabilities and the object may be non-contiguous. In this example the object will be broken into smaller contiguous DMA segments. Another example is where the device has an upper limit on its transfer size (for example an 8-bit address register) and has expressed this in the DMA limit structure (see ddi_dma_lim_sparc(9S) or ddi_dma_lim_x86(9S)). In this example the object will be broken into smaller addressable DMA segments.

ddi_dma_nextseg() returns:

DDI_SUCCESS

Successfully filled in the next segment pointer.

DDI_DMA_DONE

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

DDI_DMA_STALE

win does not refer to the currently active window.

ddi_dma_nextseg() can be called from user or interrupt context.

For an example, see ddi_dma_segtocookie(9F).

ddi_dma_addr_setup(9F), ddi_dma_buf_setup(9F), ddi_dma_nextwin(9F), ddi_dma_segtocookie(9F), ddi_dma_sync(9F), ddi_dma_lim_sparc(9S), ddi_dma_lim_IA(9s), ddi_dma_req(9S)

Writing Device Drivers