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ddi_dma_alloc_handle - allocate DMA handle

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



int ddi_dma_alloc_handle(dev_info_t *dip, const ddi_dma_attr_t *attr,
 int (*callback) (caddr_t), caddr_t arg, ddi_dma_handle_t *handlep);

illumos DDI specific (illumos DDI). dip attr callback arg handlep ddi_dma_alloc_handle() allocates a new DMA handle. A DMA handle is an opaque object used as a reference to subsequently allocated DMA resources. ddi_dma_alloc_handle() accepts as parameters the device information referred to by dip and the device's DMA attributes described by a ddi_dma_attr(9S) structure. A successful call to ddi_dma_alloc_handle() fills in the value pointed to by handlep. A DMA handle must only be used by the device for which it was allocated and is only valid for one I/O transaction at a time.

The callback function, callback, indicates how a caller wants to handle the possibility of resources not being available. If callback is set to DDI_DMA_DONTWAIT, then the caller does not care if the allocation fails, and can handle an allocation failure appropriately. If callback is set to DDI_DMA_SLEEP, then the caller wishes to have the allocation routines wait for resources to become available. If any other value is set, and a DMA resource allocation fails, this value is assumed to be a function to call at a later time when resources may become available. When the specified function is called, it is passed arg as an argument. The specified callback function must return either DDI_DMA_CALLBACK_RUNOUT or DDI_DMA_CALLBACK_DONE. DDI_DMA_CALLBACK_RUNOUT indicates that the callback routine attempted to allocate DMA resources but failed to do so, in which case the callback function is put back on a list to be called again later. DDI_DMA_CALLBACK_DONE indicates either success at allocating DMA resources or the driver no longer wishes to retry.

The callback function is called in interrupt context. Therefore, only system functions that are accessible from interrupt context is available. The callback function must take whatever steps necessary to protect its critical resources, data structures, queues, and so forth.

When a DMA handle is no longer needed, ddi_dma_free_handle(9F) must be called to free the handle.

ddi_dma_alloc_handle() returns: DDI_SUCCESS DDI_DMA_BADATTR DDI_DMA_NORESOURCES ddi_dma_alloc_handle() can be called from user, kernel, or interrupt context, except when callback is set to DDI_DMA_SLEEP, in which case it can be called from user or kernel context only. ddi_dma_addr_bind_handle (9F), ddi_dma_buf_bind_handle (9F), ddi_dma_burstsizes (9F), ddi_dma_free_handle (9F), ddi_dma_unbind_handle (9F), ddi_dma_attr (9S)

Writing Device Drivers